156 



SCIENCE. 



[N. S. Vol. Vir. No. 162. 



prominent phj'siological chemist has be- 

 come a vitalist because he could not explain 

 why the secretions differ from the blood 

 from which he thinks they are formed. He 

 overlooks, among others, the fact that the 

 protoplasm possesses the quality of semi- 

 permeability, which means that it allows 

 certain substances to pass through, and 

 others not. In my opinion, the working-out 

 of a theory of semipermeability is one of 

 the main phj'siological problems of the 

 day. 



The theory of the dissociation of Electro- 

 lytes is of fundamental importance in the 

 analysis of the constitution of living matter. 

 Pharmacology will feel its influence most 

 directly. Everything seems to indicate that 

 the specific physiological effects of inorganic 

 acids are due to the number of positively 

 charged Hydrogen Ions in the unit of solu- 

 tion, and the specific physiological effects of 

 alkalies to negatively charged Hydroxyl 

 Ions. But the universal bearing of the 

 theory of dissociation upon Physiology will 

 perhaps be best seen in the field of animal 

 electricity. An active element of living 

 matter is negatively electric to its sur- 

 rounding parts. We may assume that an 

 acid is formed in the active part, and that 

 the passive parts are neutral. The positive 

 Hydrogen Ions of the acid have a much 

 greater velocity of migration than the 

 Anions. Hence the former will diffuse 

 more rapidly into the passive tissue than 

 the Anions, and the active tissue will re- 

 main negatively charged. 



At no time since the period immediately 

 following the discovery of the law of con- 

 servation of energy has the outlook for the 

 progress of Physiology appeared brighter 

 than at present. But in order to reap the 

 full benefit of our opportunities we must 

 bear in mind that the fundamental problem 

 of Physiology is the determination of the 

 constitution of living matter, and that in 

 order to accomplish our task we must make 



adequate use of Comparative Physiology as 

 well as Physical Chemistr}'. Pathology, in 

 particular, will be benefited by such a de- 

 parture. 



Developmental Mechanics. Professor T. H. 



Morgan, Bryn Mawr College. 



In the last few years a new movement has 

 started in embryology known as Entwick- 

 lungsmechanik, developmental mechanics, 

 or rather the mechanics of development. 

 In the few minutes at my disposal I shall 

 try to show : 



I. How the term Eatwicklungsmechanik 

 arose and how it has been defined. 



II. I shall try to give an idea of the 

 kind of work that has been done. 



Roux, in 1885, first used the word develop- 

 mental mechanics and defined it as the 

 study of the causal morphology of the or- 

 ganism. It is of importance to note that 

 Roux uses the word mechanics not only in 

 its physical sense, but in its wider philo- 

 sophical meaning. Therefore, in the defini- 

 tion of developmental mechanics as the 

 study of the causal morphologj^ of the or- 

 ganism, Roux means simply that the changes 

 in form through which the embryo passes 

 are the result of a series of causes, and these 

 causes are what the new study proposes to 

 investigate. 



It may seem pretentious to state that 

 this is a new study, for every embryologist 

 must believe that the ultimate goal of his 

 work is to determine, as far as possible, the 

 causes of development. But let us look a 

 little more closelj^ into Eoux's position. 



Perhaps the problem may appear clearer 

 if we consider it in the form of a concrete 

 example. In what way, for instance, would 

 the study of the mechanics of development 

 differ from ordinary descriptive embry- 

 ology? 



We see the egg segment and then form a 

 blastula, gastrula and larva. Descriptive 

 embryology gives a series of pictures of these 



