744 



NUTRITION. 



of that capillary plexus, which forms, with the 

 convoluted lacteal tubuli, nearly the whole bulk 

 of those bodies. The writer is inclined to at- 

 tribute it, however, to another agency the 

 vitalizing influence of certain floating cells, 

 which the chyle and the blood contain ; and 

 the chief points of the evidence of this doctrine 

 will now be set forth. 



A comprehensive survey of the vital pro- 

 cesses, performed both by plants and animals, 

 enables us to bring together a number of ex- 

 amples in which cells are developed in a tem- 

 porary manner, growing, arriving at maturity, 

 and then disappearing ; apparently without 

 having performed any particular function. In 

 the albumen of the seed, for instance, this often 

 takes place to a remarkable extent. In the 

 yolk of the egg there is a similar transitory 

 developement of cells, of which several genera- 

 tions succeed each other, without any perma- 

 nent structure being the result. In the germi- 

 nal vesicle, again (according to Dr. Barry*), 

 several annuli of cells are seen to occupy its 

 cavity, when it is prepared for fecundation ; 

 and the oldest and largest of these contain 

 another generation : yet all these disappear by 

 liquefaction, as soon as the two permanent cells 

 begin to be developed in the centre. Further, 

 in the subsequent developement of all the cells 

 which are descended from these, and form the 

 ' mulberry mass," the same process is re- 

 peated ; a great number of temporary cells being- 

 produced, only to liquefy again as soon as 

 the two permanent central cells make their 

 appearance. It can scarcely be imagined by 

 the well-judging physiologist, that all this cell- 

 life comes into existence without some decided 

 purpose; and if we can assign to it an object, 

 the fulfilment of which is consistent with the 

 facts supplied by analogy elsewhere, this may 

 be reasonably considered as having a fair claim 

 to be received as a physiological induction. 



In all these instances, and in many more 

 which misj-ht be quoted, the crude alimentary 

 materials are being prepared to undergo conver- 

 sion into permanent and regularly organised 

 structures. The very first union of the inorganic 

 elements into the simplest proximate principles 

 is ed'ected by the cell-life of plants. The change 

 of these principles into the peculiar compounds 

 which form the characteristic secretions of 

 plants, is another result of their cell-life. And 

 there seems equal ground for the belief, that 

 the change of the proximate principles, sugar 

 and gum (of which the latter appears to hold 

 the same place in the vegetable economy that 

 albumen does in the animal), into the peculiar 

 glutinous sap, which is found wherever a forma- 

 tion of new tissue is taking place, is equally 

 dependent upon the agency of cells. The 

 process is probably commenced in the leaves ; 

 but as the ordinary descending sap, which is 

 the product of their elaboration, is not so re- 

 markable for its plasticity as the fluid drawn 

 from certain rapidly growing parts, it seems 

 probable that a local agency takes place in 

 these, analogous to that which we shall be able 



* Embrj-ological Researches, third series. 



to trace in certain conditions of the animal 

 economy. Thus, the starchy fluid which is 

 contained in the ovule, previously to its fecun- 

 dation, is probably not in the state in which it 

 can be immediately rendered subservient to the 

 nutrition of the embryo; and the developement 

 of successive generations of cells, which exert 

 upon it their vitalizing influence, may be rea- 

 sonably regarded as the means by which the 

 requisite change is effected. Exactly the same 

 may be said of the albuminous matter con- 

 tained in the yolk of the egg, which is certainly 

 not in a condition in which it can be imme- 

 diately applied to the purposes of nutrition ; 

 and its conversion may be regarded as com- 

 mencing with the developement of transitory 

 cells within its own substance, and as being 

 completed by means of the cells forming the 

 inner layer of the germinal membrane, by 

 which it is subsequently taken up and intro- 

 duced into the current of blood flowing through 

 the vascular area. A similar purpose is proba- 

 bly answered by the transitory cells developed 

 within the germinal vesicle; and by those 

 which appear at a similar period in the evolu- 

 tion of the descendents of the " twin cells '' 

 produced in it. 



Many other examples of a similar process 

 might be adduced, but they would all lead to 

 the same general conclusion, which harmonizes 

 well with the important principle of general 

 physiology, that the higher the grade of struc- 

 ture ultimately to be attained by any part, and 

 the more permanent its character is destined to 

 be, the longer and more elaborate are the preli- 

 minary stages of its evolution. As an instance 

 of this law, which bears a remarkable analogy 

 with the facts just recorded, we may advert to 

 the production of a temporary respiratory ap- 

 paratus in the higher plants and animals, cor- 

 responding with that which is permanent in 

 the lower parts of the scale. There are proba- 

 bly cases, however, in which cells are very 

 rapidly called into existence, without that pre- 

 paratory elaboration of their nutrient materials, 

 which we regard as due to the vital operations 

 of a preceding generation. Thus the Bovista 

 giganteum, a large fungus of the Puff-ball 

 tribe, lias been known to increase, in a single 

 nig/it, from a mere point to the size of a huge 

 gourd, estimated to contain 47,000,000.000 

 cellules. In such a case it is difficult to sup- 

 pose that any but the most rapid mode of 

 generating cells can have been in operation; 

 and the idea that these could not have been 

 developed by any such elaborate process as 

 that just alluded to, is borne out by the fact of 

 their extremely transitory character, the decay 

 of such a structure being almost as rapid as its 

 production. The same may be remarked of 

 those fungous growths in the animal body 

 which sprout forth most rapidly. Hence the 

 apparent exception assists in proving the rule. 



\Ve have thus a class of facts which indicates 

 that the conversion of the chemical compound 

 into the organizable principle {\\eaplastic into 

 the plastic material is effected in the parti- 

 cular situations where it is most wanted by the 

 vital agency of transitory cell-life; that is, by 



