490 



NATURE' 



[September 23, 1897 



two individuals (or parts of tliem) are so united as to 

 have a common vascular system ; and the connection 

 which this result seems to suggest, of a direct relation 

 between chemical change in the blood and histological 

 dififerentiation in the tissues, opens up a promising field 

 for further work. 



The hind end of a larva, grafted in the manner 

 described on to the body of a second larva, can be 

 reared up to the time of metamorphosis. It seems to 

 grow normally, up to the point of section, except that 

 its rectum, if present, communicates with that of the 

 stock. There is apparently little or no nervous con- 

 nection between stock and graft, since gentle stimulation 

 of the graft causes reflex movement only of that tail, the 

 stock remaining quiescent, and vice versa. 



In a similar way an excised head, grafted into the 

 ventral surface of a second larva, may remain without 

 nervous connection with the stock. The two are con- 

 nected chiefly through the oesophagus of the graft, which 

 fuses with and opens into the alimentary canal of the 

 stock, and by the blood vessels. Such a grafted head 

 shows snapping- and respiratory movements, which are 

 independent of those performed by the head of the stock, 

 and have a different rhythm. As before, the grafted 

 •head may be larger or smaller than the head of the 

 stock, but the rate of histological differentiation is the 

 same in both. 



These experiments go to show that provided a proper 

 food supply be furnished, any portion of a frog larva, after 

 the closure of the medullary folds, will develop in very 

 nearly the same way, whether it be in its normal relation 

 to the rest of the embryo or not, up to the period of 

 metamorphosis. Indeed, the death at metamorphosis 

 appears at least in many cases to be simply caused by 

 mechanical injury which the stock inflicts upon the 

 graft, by scraping it against foreign bodies — a phe- 

 nomenon obviously connected with the absence of 

 nervous communication between the two. It is especially 

 pointed out that the position of the grafted portion has 

 no obvious influence on the result : so that nothing like 

 the " polarity " observed by Wetzel in his experiments 

 with Hydra, and by others in similar cases, can be seen 

 in the larval frog. 



The cases so far mentioned involve the union of com- 

 paratively small portions of one larva with the nearly 

 complete body of a second. More complicated unions 

 are effected by slicing a small piece from the ventral or 

 from the dorsal surface of each of two larv£E, and joining 

 the two by their wounded surfaces, so that two nearly 

 complete larva; are united. The relation between such 

 components follows the same rule as that found to hold 

 for the unions already described : the rate of growth 

 may differ to a considerable extent, but the rate of his- 

 tological differentiation is always the same. In these 

 cases, and in those presently to be mentioned, corre- 

 sponding organs, which are in contact at the point of 

 section, unite ; and hollow organs, such as gut, nervous 

 system, heart, coelom, unite in such a way that the cavity 

 of one component communicates with the homologous 

 cavity of the other. In ventral unions, therefore, the two 

 components have a common alimentary cavity, a common 

 coelom, and often a common heart ; in dorsal unions 

 they have a common neural cavity, and so on. When 

 NO. 1456, VOL. 56] 



corresponding organs unite, there is generally complete 

 histological continuity of the characteristic tissue of the 

 organ from one component to the other, without any 

 formation of scar tissue, so that nerve fibres run across 

 the line of junction of two brains ; gastric epithelium 

 evenly across the junction of two stomachs, and so on. 



Detailed descriptions of many of these unions are 

 given, but some of the most interesting are as yet 

 withheld. Some of the results of these unions have 

 been successfully reared through the metamorphosis, and 

 are now frogs. The reasons which have prevented Prof. 

 Born from killing these creatures in order to describe 

 their structure will be easily understood. 



A third series of specimens is obtained by uniting the 

 front portion of one larva to the hinder portion of 

 another ; and where about each component contains 

 about half a larva, the result seems to be almost indis- 

 tinguishable from a normal individual. A case is de- 

 scribed in which the anterior two-thirds' of one larva was 

 united with the posterior two-thirds of the other ; the 

 resultant creature has been reared through the meta- 

 morphosis, and is now a frog with a trunk of abnormal 

 length. 



The way in which corresponding organs unite across 

 the plane of section in cases of this kind is truly remark- 

 able, and induces a belief in some adjustment of the 

 parts after apposition. For example, the pronephric 

 ducts unite so that the cavity of the anterior portion of 

 the duct communicates with that of the posterior portion ;. 

 and in spite of the very wonderful manipulative skill 

 which Prof. Born must have attained, it is difiicult to 

 believe that such minute structures can have been even 

 frequently adjusted by him with absolute accuracy at 

 the time of operation ; indeed, in the case of the much 

 larger spinal cord there are sometimes obvious indica- 

 tions of a readjustment. 



The last series of experiments described demonstrates 

 the possibility of obtaining some of the results by joining 

 larvye or portions oflarvas belonging to different species,, 

 or even to different genera. Unions are figured between 

 Rana esculenta and Bombinaior igneus. 



The experiments are not yet concluded, and it would 

 be presumptuous to do more than describe them ; at the 

 same time, their interest is so great that it has seemed 

 worth while to do this at considerable length, 



W. F. R. Weldon. 



EFFECTS OF HIGH ALTITUDE UPON MAN, 

 j La Cure cV Altitude. Par le Dr. Paul Regnard. Pp. 

 ' viii -I- 436. 8vo. 29 plates; no figures in the text. 

 (Paris : Masson et Cie., 1897.) 



THE hardihood and endurance of mountaineers has 

 been always celebrated. A Swiss Protestant 

 clergyman, Kraenbuhl, noticed a great difference be- 

 tween children from the mountains and those of certain 

 schools in Zurich and Bern. He arranged for some of 

 the weakly children from the towns to live at Beaten- 

 berg in the mountains, and after some months had the 

 satisfaction of seeing these children much improved ; 

 in fact, completely changed for the better. This occurred 

 about 1850, and attracted many delicate persons to 



