i2 POPULAR SCIENCE MOXTHLY 



Fifth and last, I should like to gather under the head of morpho- 

 physics a number of researches, nearly all of which are very recent, 

 and which tackle the doctrine of the chemical and physical causes of 

 development. These researches have been largely experimental in 

 character, and though we are only at the beginning of this sort of 

 work, vet the results already obtained are of the highest value and 

 make us hope for far greater results to come. 



There should be added logically a sixth heading for the physiology 

 of the embryo, but so little has been done and so little is doing in this 

 part of biology that only in the future can this logically correct sixth 

 division correspond to a field of active research. Here poverty of 

 achievement makes further present consideration by us superfluous. 



It is unnecessary to argue in order to prove to you that the study 

 of generation is of importance to the medical man. The results which 

 embryologists have already offered in solving some of the problems of 

 generation form part of the stock in trade of every practitioner, for 

 every one must know something of the uterus and placenta, must 

 know that there is no communication between the fcetal and maternal 

 circulation — no passage of the blood from the mother to that of the 

 child : that there is no machinery for the making of so-called maternal 

 impressions; that conception depends primarily upon the fusion of 

 two living elements, the ovum and spermatazoon, which arise as living 

 and integral parts of the parental bodies, and must know thus that 

 there is a continuity of life, an earthly immortality, and that from 

 generation to generation life is uninterrupted. All these notions and 

 many others derived from embryology are now-a-days part and parcel 

 of every physician's information, and it is hard to realize that a short 

 time ago many of these facts were unknown to us. I believe that 

 in the course of the next few years many new discoveries concerning 

 generation will be made which will in their turn become familiar to 

 all. I expect especially in regard to the subject of heredity a great 

 increase in our knowledge, because the subject has attracted many 

 investigators and some notable results have already been achieved. I 

 may instance the history of the germ cells in which I have been espe- 

 cially interested. Professor Moritz Xussbaum on the basis of certain 

 observations which he had made, put forward in 1880 the theory of 

 germinal continuity. He pointed out that there is noteworthy evi- 

 dence in the development of various animals tending to show that the 

 germinal cells from which the sexual products arise are separated off 

 very early from the other cells of the embryo and undergo very little 

 alteration until the time comes for them to be transformed into sexual 

 elements, male or female, as the case may be. Dr. F. A. Woods, work- 

 ins in mv laboratorv upon the embrvos of dog-fish brought the first 

 conclusive demonstration that Xussbaunvs theory is true for a verte- 

 brate. He found that the germ cells are set apart, have a distinct 



