AND OF THE PHYSICAL SCIENCES. 



87 



to the hands, where it is found beneath the epidermis, but is also sometimes met with 

 on the feet, in the arm-pits, and other places. It is never found on persons affected 

 with any other cutaneous disease than itch. The insects are all destroyed after the 

 sulfuro-alcaline ointment has been applied ; but the patient may not be still cured, 

 for the eruption may remain, unless it be properly treated. 



Insects removed from an affected to a sound person, multiply on the skin of the 

 latter, when presently the eruption appears. M. Gras several times communicated 

 the disease in this manner ; once, at the desire of Dr Pariset, secretary of the Aca- 

 demic de i\I«dicine, when it produced a sanatory revulsion in a young girl who had 

 fallen into a state of stupor. On the other hand, he several times tried to inoculate 

 himself with the serum of the itch vesicles, but without success. He therefore con- 

 eludes that the sarcoptes is the sole agent in producing the contagion of itch, which 

 is not contracted unless that animal or its eggs adhere to the skin or clothes of per- 

 sons coming into contact with those having the disease. 



The number of insects on a person has no relation to the extent and intensity of 

 the eruption ; for sometimes not more than five or six are found on individuals co- 

 vered with vesicles and pustules ; and again, a hundred have been taken from the 

 faands of a person, who yet had only a few vesicles. 



BOTANY. 



Alleged Irritability evinced by the Stems of Plants when slit — Mr 

 Goldin"" Bird has endeavoured, in Loudon's Magazine for February, to explain the 

 c-etraction observed by the two portions of a slit stem or stalk, on the principle of 

 endosmosis. If a portion of the stem of an herbaceous exogenous plant be divided 

 longitudinally, the division extending to the length of about two inches, the divided 

 portions will instantly separate from each other to the distance of an inch or even 

 more. The same thing occurs if the young shoots of woody stems are slit. Dr H. 

 Johnson of Shrewsbury, who first attempted to explain this phenomenon, attributed 

 it to the vital irritability of the plants, in consequence of its absence in some which 

 are very elastic, and in the woody parts of stems. Mr Bird, however, conceives 

 that it may be explained in another manner. Dutrochet has shown, that when a 

 fluid, as water, or a weak saline solution, is inclosed in an organized membrane, as 

 a piece of bladder, or placed in a glass tube closed by a piece of membrane, and im- 

 mersed in a solution of sugar, the bladder or glass tube is rapidly emptied; but if, 

 on the contrary, the bladder or tube be filled with syrup, and immersed in distilled 

 water, the reverse takes place, the bladder becoming completely turgid. From those 

 facts he inferred, 1st, That when a fluid of low specific gravity, inclosed in an or- 

 ganic membrance, is immersed in one of greater density, the membrane becomes 

 rapidly emptied, in consequence of a current being set up from the lighter to the 

 denser fluid ; and, 2(/, That when a dense fluid is inclosed in a membranous reser 

 voir, and immersed in a fluid of a lower specific gravity, a current is set up, whereby 

 the membrane becomes distended by a supply of fluid from without. The current 

 from within to without, Dutrochet named endosmose ; that from without to within, 

 exosmose. Now, on this principle, rather than on the irritability of the plants, Mr 

 Bird accounts for the following facts observed by him. 



1. A piece of the stem of Lamium album, on being longitudinally divided to the 

 extent of three quarters of an inch, immediately exhibited a divergence of its seg- 

 ments, which separated to half an inch. 2. Another piece, similarly treated, showed 

 the same result, fig. 1 ; and, on being immersed in distilled water, continued to curve 

 in a still greater degree, fig. 2. 3. This piece was then immersed in a weak solu- 

 tion of sugar, when, in the course of an hour, the segments had approached so closely 

 as to touch each other, fig. 3. When replaced in water, the segments again di- 

 verged ; and so on repeatedly. 4. The upper part of the stem of a young plant, 

 that had stood for twenty-four hours with its lower portion immersed in water mixed 

 with hydrocyanic acid, showed no divergence on being slit. 5. The same piece was 

 placed in distilled water, when, in six hours, the divided portions separated to the 

 extent of half an inch. "When remuved, and immersed in syrup, it showed a still 

 greater divergence. 6. Apiece of the stem of StacfiT/s puhtstr is, removed from 

 near the root, was left for some days exposed to the air, and when dry was slit, but 

 did not exhibit the least appearance of divergence. 7. A portion of this dried piece, 

 on being placed in weak syrup, nearly regained its natural stage of turgescence in 

 about twelve hours ; when, on being slit at its upper part, it immediately manifested 

 tlivergence ; and which increased on its being immersed in water. 



Dr Bird's explanation is to the following effect: — That the property of divergence 

 does not depend upon vital irritability, as Dr Johnson assumed, is shown by experi- 

 ments 5 and 7, in which the property was restored, by artificial means, to stems de- 

 prived of vital influence, by being isolated from the plants bearing them, and submit- 

 ted to the deleterious influence of a poison, or to desiccation. That it is not caused 

 by elasticity is evident, seeing that the property of divergence is absent in the most 

 elastic parts of plants, as true woody fibre, rattan cane, &c., and present in the most 



delicate herbaceous plants, as well as in the most inelastic. Dutrochet has shown, 

 that the valves of the pericarp of Impatiens Balsamina, which, when mature, sepa- 

 rate from each other, and become considerably curved inwards, are composed of a 

 vesicular tissue, of which the vesicles nearest the external are considerably larger 

 than those nearest the internal face of the valves. The tissue being injected from 

 an accumulation of sap, all the cellules become turgid, and the larger ones occupy a 

 greater space than before. Their complete distension being, however, prevented by 

 the more compact tissue formed by the aggregation of tne minuter cells, the whole 

 valve assumes a tendency to curve in such a manner, that the external portion, or 

 that composed of the larger cells, may occupy the convex part of the curve ; and 

 this tendency to curve is obeyed as soon as the resistance of the opposite valve is re- 

 moved by a slight touch or otherwise. This explanation may be applied to the phe- 

 nomenon in question. The vesicular tissue of the Lamium and other plants is more 

 minute towards the circumference, the internal part being composed of much larger 

 cellules. When a stem possessing this structure is in perfect vigour, its vesicular 

 tissue is injected with sap ; the larger central cells become considerably distended, and 

 press upon the smaller cells, which, resisting the pressure, give to the larger cells a 

 tendency to separate, and occupy a greater space in consequence of this distension ; 

 their separation being, however, prevented by their intimate lateral organic connection. 

 But when this bond of union is severed, by an incision or otherwise, the segments 

 instantly separate, and curve in such a manner, that the internal portions, or those 

 made up of the larger cellules, form the convex part of the curve, and thus leave 

 more room for their distension ; whilst the external portions, formed of a more com- 

 pact tissue, occupy the concave parts of the curve, in consequence of their not becoming 

 distended so easily or readily as the tissue nearest the axis of the plant. 



This explanation is considered to be in perfect accordance with the result of expe- 

 riment ; for, on immersing the piece of stem, when the segments have separated to a 

 certain extent, in water, which is a fluid of lower specific gravity than the sa^) in the 

 cells, endosmosis ensues, whereby a quantity of water is forced into the already turbid 

 cells, which, consequently, become more turgid, and the curvature increases ; and on 

 removing the piece of stem into syrup, a much denser fluid than sap, exosmosis, for 

 reasons already explained, ensues ; the cells become emptied, and the separated por- 

 tions recover their former rectitude ; the elasticity of the woody fibre presentj also, 

 probably assisting. The reason why poisons prevent the divergence is, that as they 

 destroy the vital energy of the plant, they prevent the cells from becoming distended 

 with sap to an extent sufficient to cause their separation ; but, on placing the piece of 

 stem in water, endosmosis occurs, and the divergent property is developed. But 

 when the piece of stem used had been previously dried, the cells were emptied of their 

 sap, and it was necessai-y to fill them aitificially with a tolerably dense fluid, as syrup, 

 before they became sufliciently injected to cause the separation of the segment, on 

 making a longitudinal incision. 



I\lr Bird, therefore, is decidedly of opinion, that the divergence is the result of a 

 purely physical action^ independent of vitality ; and in this we agree with him, al- 

 though it is obvious that a much simpler and equally satisfactory explanation of the 

 phenomenon can be given. 



The plants found to exhibit it are possessed of a vascular, a fibrous, and a vesicular 

 tissue. The latter occupies the central parts exclusively ; while the woody fibres 

 occur towards the exterior, as do the vessels properly so called. Tliis arrangement 

 is represented by the diagram, fig, 4, in which «, a, indicate the surface of the stem, 

 i, /i, its axis. Now, the woody fibres near a, not being extensile, and the cellules 

 at b, being dilatable, it will necessarily follow, that when a section of the stem, such 

 as that represented by the figure, is made, the cellules being filled with fluid, or va- 

 pour, which readily passes from the one to the other, the larger inner cellules, in con- 

 sequence of the pressure caused by the unyielding cuticle and herbaceous tissue which 

 compressed the interior when the stem was entire, being now allowed to expand to 

 their full size, or in some degree, while the outer cellules are bound together by the in- 

 extensile woody fibres, the curvature outwards of the section is a necessary result, so 

 long as moisture is supplied by the unslit portion of the stem, or communicated from 

 without, this fluid ascending on the principle of endosmose. When, as in experiment 

 2, the sht stem is immersed in water, the divergence is increased on the same prin- 

 ciple ; but when, as in experiment 3, a denser fluid is substituted, exosmose takes 

 place in the vesicular tissue, in consequence of which, the pressure is removed from 

 the larger vesicles, which, by their elasticity, regain their original size. In the plant, 

 experiment 4, whose lower parts were destroyed by poison, the upper not bavin"- re- 

 ceived a supply of fluid to replace the quantity evaporated in twenty-four hours, no di- 

 vergence could ensue on slitting it; but, as in experiment 5, should it be filled with 

 fluid, it diverges as explained above. For the reasons stated, a dried piece of stem, 

 experiment 6, can of course undergo no change ; but if restored to its natural state 

 as in experiment 7, it exhibits the usual phenomenon. In accordance with this ex- 

 planation is the fact, that woody stems when slit do not diverge, because all their parts 

 are equally bound together by firm longitudinal fibres, as well as that of purely cellular 

 plants, such as Fucus palmatus, exhibiting no divergence. 



Wherefore, we neither agree with Dr Johnson, in considering the divero^ence or 

 curvature in question us a result of vital contractibility or irritability ; nor with Mr 

 Bird, in attributing it solely to the larger vesicles being more readily distended than 

 the smaller. 



GEOLOGY. 



Fossil Skull of Dinotherium Giganteum, — M, Kaup has addressed to M. 

 Blainville a letter, giving intimation of the discovery of a perfectly-preserved head of 

 Dinotherium giyanieum, at Eppelstein, by a society, at the head of which is Dr 

 Khppstein, who intends to prefix a geological introduction to the description and 

 figure about to be published by the gentleman above-named. The expense of dis- 

 engaging the head having been very considerable, the society intend to send it first 

 to Paris, and afterwards co London, to be exhibited to the public. It is probable, 

 however, that it will be purchased by the Academic des Sciences. 



