NOVEMBEK 24, 1905.] 



SCIENCE. 



60 1 



cases of salt poverty, sodium chloride as 

 well (these being materials which the or- 

 ganism can not afford to lose), while at the 

 same time these epithelial cells, like those 

 of the intestines, have also to perform the 

 duty of excreting the combined substances 

 of the blood by means of their specific 

 secretory activity. 



Diuresis, therefore, represents the fusion 

 of two principal processes — one concerning 

 the gomeruli, which is in its main features 

 mechanical in its nature ; the other pertai^ 

 ing to the urinary tubules, which is not yet 

 explicable on any physico-chemical hypoth- 

 esis. The process of resorption from the 

 urinary tubules has a distinctly biological, 

 that is, teleological character; water and 

 salt are only reabsorbed when the organism 

 does not possess these in excess. If one 

 administers an abundance of water, the 

 urine acquires a highly watery character, 

 while after the administration of an abun- 

 dance of sodium chloride there is a failure 

 on the part of the tubules to reabsorb salt, 

 as Loewi has shown. The process of re- 

 absorption adapts itself, therefore, to the 

 requirements of the organism. 



Although I believe that the theory of 

 renal function which I have here presented 

 is the one which has the best experimental 

 foundation, I readily concede that it leaves 

 many facts still unexplained. For ex- 

 ample, it is difficult by means of this hy- 

 pothesis to explain the constituti6n of the 

 urine in diabetes insipidus as well as the 

 complete retention of chlorine under cer- 

 tain conditions, and I fancy that we shall 

 have to suppose, as Cushny has done, that 

 there is some kind of combination of so- 

 dium chloride with the blood tissue which 

 hinders its filtration. The theory of di- 

 uresis and the action of diuretic drugs fur- 

 ther possesses a practical interest. If, for 

 example, it be true that caffeine acts di- 

 uretically through local specific dilation 



and not through irritation of the secretory 

 cells, as was formerly supposed, then, as 

 Loewi thinks, we are justified in its admin- 

 istration during long periods in the course 

 of nephritis in which, in many instances, 

 the vessels of the kidneys are abnormally 

 contracted. And there is some reason to 

 believe that the vasodilator action of the 

 caffeine not merely induces an increased 

 diuresis but exerts a favorable influence 

 upon the pathological condition of the kid- 

 ney itself. 



In conclusion, I desire to express my ap- 

 preciation of the courteous attention you 

 have accorded me. Hans Meyer. 



THE EVOLUTION OF SPECIES THROUGH 

 CLIMATIC CONDITIONS. 



In a recent article in Science,^ entitled 

 'The Origin of Species through Isolation,' 

 President David Starr Jordan has pre- 

 sented much evidence bearing upon the 

 influence of geographical isolation in the 

 formation of species and races of animals 

 and plants. He dwells especially upon the 

 agency of barriers in interrupting the flow 

 ■ of life and isolating groups of individuals 

 of a species, which groups of individuals, 

 either with or without material change in 

 the conditions of existence, 'may become 

 in time an entirely distinct species if the 

 barrier is really insurmountable.' This is 

 impliedly recognized as only one of various 

 influences that tend to modify species, but 

 in this connection, in marshalling the evi- 

 dence in favor of the proposition of the 

 origin of species through isolation, hardly 

 any reference is made to the part played 

 by other agencies in the evolution of new 

 forms. In this way, rather undue impor- 

 tance is given to a single and well-recog- 

 nized factor in the problem of evolution. 

 The purpose of the present paper is not to 



^ N. S., Vol. XXII., No. 566, November 3, 1905, 

 pp. 545-562. 



