435 THE SPLEEN. [BOOK n. 



out. While erection of the nipple ceases when the spinal nerves 

 which supply the breast are divided, the secretion continues, and 

 is not arrested even when the sympathetic as well as the spinal 

 nerves are cut. 



The Spleen. 



The Spleen may be wholly removed from an animal without 

 any obvious changes in the economy taking place : the functions of 

 the rest of the body appear to go on unimpaired. We are obliged 

 to assume that some compensating actions take place; but what 

 those actions are we do not know, and we are left at present by 

 these experiments almost completely in the dark as to the functions 

 of the spleen. The most that has been observed is a slight increase 

 in the lymphatic glands, and in the activity of the medulla of bones 

 (see p. 29), but even this is doubtful. 



After a meal the spleen increases in size, reaching its maximum 

 about five hours after the taking of food ; it remains swollen for 

 some time, and then returns to its normal bulk. In certain diseases, 

 such as in the pyrexia attendant on fevers or inflammations, and 

 more especially in ague, a similar temporary enlargement takes 

 place. In prolonged ague a permanent hypertrophy of the spleen, 

 the so-called ague-cake, occurs. 



The turgescence of the spleen seems to be due to a relaxation 

 both of the small arteries and of the muscular bands of the 

 trabeculse ; to be, in fact, a vaso-motor dilation accompanied by a 

 local inhibition of the tonic contraction of the other plain muscular 

 fibres entering into the structure of the organ, the latter, at all 

 events in some animals, being probably the more important of the 

 two. And the condition of the spleen, like that of other vascular 

 areas, appears to be regulated by the central nervous system, 

 the digestive turgescence being altogether comparable to the 

 flushed condition of the pancreas and of the gastric membrane 

 during their phases of activity. 



The application of the plethysmographic method to the spleen, 

 carried out in the way which we described in speaking of the 

 kidney (p. 398), has revealed certain interesting phenomena. 



A 'spleen curve* Fig. 66 taken in the same way as a 'kidney 

 curve' brings to light the following facts. The volume of the 

 spleen does not vary, as does that of the kidney with each pulse 

 wave. The kidney curve as we have seen, p. 400, gives clear 

 indications of each heart beat, but the spleen curve shews only 

 gentle undulations, obviously due to the respiratory movements. 

 This difference corresponds to the difference in the vascular 



