OPENING ADDEESS. 19 



was approached from the functional side. Suppose the 

 gland and its cells are worked so hard that they are 

 exhausted of their potential secretory activity, and they 

 are then compared as to structure with others in the full 

 vigour of secretion. Surely they must look different, 

 especially if they are examined in the living state. 

 The pancreas of the rabbit was so examined by Kiihne 

 and Lea, and it was observed that the exhausted cell 

 was small, whilst the manufacturing cell was not only 

 large but full of granules. 



If the cells are fixed by microscopic reagents, then, as 

 a rule, they are altered ; the older methods of hardening 

 tissues reduce their cells all more or less to the same 

 common denomination. By the use of osmic acid, alone 

 or in combination with various reagents, it is now found 

 possible to fix them so that their death will not essentially 

 alter their living appearance, and structural features have 

 now been found in the pancreas, the salivary glands, the 

 liver, the gastric mucous membrane, etc., which features 

 vary pari passu with the variation in the chemical pro- 

 perties of their secretion. Instead of Physiology following 

 in the wake of Histology, it has now become the guide, 

 pointing the direction which microscopic work should take. 

 As Sanderson said in his Newcastle address to the 

 Biological Section, at the British Association, in 1889 : 

 " Whereas hitherto the greater part of the work has 

 consisted in the interpretation of facts arrived at in the 

 first instance by anatomical methods of research, Histology 

 once the guide of Physiology has now become her hand- 

 maid." 



I can think of no recent instance more striking than 

 that of the structural changes in the cells of the mammary 

 gland accompanying the various phases of the secretion 

 of milk. Milk contains all the essential constituents of 



