OCTOBER 29, 1897. ] 
indicates that our knowledge of how these 
forces are exerted and how the energy of 
the cell is transformed is hypothetical or 
wanting; and not until this deficiency is 
made up can the physiological experiment 
be interpreted in simple physico-chemical 
terms. This was Heidenhain’s teaching. 
The study of the secretion of the bile 
early claimed the attention of Heidenhain 
and his pupils. Besides contributing valu- 
able data on the composition of this fluid 
and the conditions modifying its discharge 
from the liver, he made comparative meas- 
urements of the pressure under which the 
bile is secreted and the pressure in a branch 
of the superior mesenteric vein. In finding 
the bile pressure invariably twice as high 
as the blood pressure in the portal vein, he 
demonstrated for the bile, as Karl Ludwig 
had done in 1858 for the saliva, that secre- 
tion is not a mere act of filtration and thus 
a mechanical result of blood pressure. 
The year 1866 marked the beginning of a 
series of papers which have contributed 
more than all others to bring renown to the 
Breslau physiologist and which mark a dis- 
tinct advance in physiological knowledge. 
Irefer to the brilliant researches on the 
salivary, gastric, pancreatic and other 
glands, in which physiological experiment 
was successfully combined with histological 
investigation. The facts discovered have 
been verified by numerous observers and 
are familiar to every biologist. Here was 
shown for the first time that in the 
secreting glands structural changes go on 
hand in hand with functional processes. 
With characteristic patience and thorough- 
ness the various glands were made the sub- 
ject of an exhaustive study and each new 
field afforded new problems and new results. 
For the salivary glands it was shown that 
the production of specific constituents and 
the secretion of water are more or less inde- 
pendent processes and thus the idea of dis- 
tinct trophic and secretory nerves was intro- 
SCIENCE. 
647 
duced into physiology. For the pancreas, 
too, Heidenhain indicated indirectly the 
existence of specific secretory fibres, which 
Pawlow has since directly proved. The dis- 
tinction between serous and mucous glands 
was also pointed out on the basis of struc- 
tural, chemical and functional differences. 
In his studies on gastric and pancreatic 
secretion Heidenhain pursued with success 
the plan which had been found valuable in 
the case of the salivary glands, and we owe 
our knowledge of the minute structure of 
these organs during rest and activity in 
large part to the labors of this investigator. 
The fundus and pyloric fistulee are examples 
of the valuable methods of research devel- 
oped by him. Almost simultaneously with 
Rollet he announced the distinction between 
the central and parietal gastric cells; his 
discovery, in 1875, of the so-called ‘zymogen’ 
of the proteolytic enzyme of the pancreas 
has been followed by announcements of pre- 
cursors for other ferments and has added a 
new idea to the theory of secretion. 
Contrary to the older theory of Bowman, 
Ludwig had taught that the urineis ex- 
ereted entirely through the epithelium of 
the Malpighian capsule, the fluid being 
eliminated in consequence of purely me- 
chanical filtration, and undergoing a subse- 
quent concentration by the diffusion of water 
into the lymph spaces surrounding the kid- 
ney tubules. Heidenhain’s experiments first 
demonstrated conclusively that the epithe- 
lial cells of these tubules take a prominent 
part in renal secretion. He didnot fail to 
note, at the same time, the close depend- 
ence of secretory activity upon blood flow, 
i. €., upon material for cellular work and 
upon the presence of oxygen ; thus was em- 
phasized the teleological significance of 
Claude Bernard’s discovery that the blood 
vessels of secreting glands are greatly di- 
lated during glandular activity. 
The researches to which the later years 
of Heidenhain’s life were devoted followed 
