164 SCIENCE PROGRESS. 



blood streaming through it. Nay, he showed that secretion 

 might take place in a decapitated animal, provided the 

 nerve going to this gland be stimulated. Numbers of his 

 pupils continued to work at salivary secretion, both from its 

 physiological aspect, e.g., Becher, Rahn, Spiess, and its 

 histological. 



Indeed Ludwig's contributions to the physiology of the 

 excretions may be regarded as amongst his most important 

 contributions. In connection with the salivary glands, his 

 histological investigation paved the way for important ex- 

 perimental results. With Gianuzzi he investigated the 

 structure of the salivary glands, and in his celebrated paper, 

 " Ueber den Einfluss d. Beschleunigung d. Blutsstromes 

 auf die Absonderung des Speichels," Gianuzzi discovered 

 those curious bodies in the mucous salivary glands which 

 still bear his name and are called "demilunes" or "Gianuzzi's 

 crescents". There are numerous and classical investigations 

 on the secretion of saliva. Indeed so late as 1889 we find 

 Novi investigating "Die Scheidekraft d. Unterkiefer druse". 

 But while Ludwig's investigations not only completely trans- 

 formed the theory of secretion, by his investigations he added 

 an entirely new class of nerves to those already known, 

 viz., those known now as "secretory nerves". 



Up to the time that Ludwig stimulated the nerves to 

 the salivary glands, physiologists were acquainted only with 

 contraction of muscle resulting from stimulation of the peri- 

 pheral end of a divided nerve. That the nervous system 

 affected the secretions and excretions had been known from 

 time immemorial— for example, the flow of tears under emo- 

 tion, the arrest of salivary secretion under the influence of 

 fear — but these results might be due to the supply of blood 

 or other cause. When Ludwio- be^an his researches, all 

 these and other secretions were regarded merely as due to 

 simple filtration of fluids through different membranes. 

 Ludwig proved that this is not so, but that the nerves 

 act directly upon the gland cells themselves, and thus re- 

 gulate the chemical metabolic processes going on within the 

 secretory cells. Ludwig's great contemporary, Claude Ber- 

 nard, discovered the " vaso-motor nerves," or those nerves 



