ESSAY-REVIEWS 683 



individual and the species. And if Mr. Shand, when speaking of an internal 

 rather than external stimulation, is willing to accept a qualitative bio-chemical 

 change in the blood as the exciting cause of desire to gratify the appetites, 

 then physiologists will agree with him. But can this bio-chemical change 

 excite a sensori-motor instinctive mechanism apart from feeling, if we admit 

 that feeling does not exist in the lower medullary centres ? To answer this 

 question it is necessary to see what physiological evidence there is of bio- 

 chemical changes in the blood playing an important part in exciting instinctive 

 protective motor reaction. Mr. Shand cites the act of sucking in the new-born 

 infant as being aroused by internal stimulation. The important part that bio- 

 chemical changes play in the vital processes of reproduction has been proved by 

 physiological experiments. Thus Goltz showed that at the proper time a bitch 

 that had become pregnant after a large part of the spinal cord had been removed 

 gave birth to a litter of puppies. Paul Bert long ago showed that the mammary 

 glands of a goat, that had had all the nerves divided, increased in size and 

 prepared for lactation during pregnancy. Physiologists have shown that the 

 corpus luteum, the tissue which occupies the place of the ripe ovum after its 

 discharge from the Graafian follicle, liberates an internal secretion which acts 

 as a bio-chemical stimulus in the blood to the mammary glands and the uterus ; 

 it also excites certain cells in the pituitary gland to active proliferation ; it 

 causes enlargement of the thyroid and parathyroid glands, increasing their 

 function ; and it increases the quantity of lipoid substances in the cortex of the 

 suprarenal glands. There is thus proved to be a bio-chemical association of 

 the ductless glands and the reproductive organs. In the testis, as well as in the 

 ovary, there are really two glands, the one generative, producing germs which 

 escape by a duct, the other ductless (interstitial), the cells of which secrete a bio- 

 chemical hormone, which (from the embryonic state onwards) passes into the 

 blood and is carried to all the cells of the body, making dominant the correspond- 

 ing male or female secondary sexual characters. It is also the source of vague 

 unconscious sexual desires which at puberty become so strong as to cause a 

 complete mental revolution of the individual. 



Now McDougall, in referring to the sucking infant, says the odour of the milk 

 is the first stage in the act of sucking, and it is this which excites an instinctive 

 search ; but we know that an anencephalous monster is capable of the act of 

 sucking. Seeing that it has no great brain, can we assume that it is excited by 

 the odour of milk? Why should not a bio-chemical change in the blood 

 occasioned by the entirely changed conditions of life of the child after birth be the 

 exciting cause ? In support of this influence of the condition of blood in the 

 medullary centres acting as an exciting cause, we know that an animal with the 

 medulla oblongata separated from the brain above and from the spinal cord 

 below evinces by respiratory movements of the nostrils and the larynx that a 

 condition of anoxaemia suffices automatically to excite the motor mechanism of 

 respiration in the medulla. When a person loses a large quantity of blood 

 he feels the pangs of thirst ; this feeling is not removed by moistening the mouth, 

 but it is by the introduction of a large quantity of saline solution subcutaneously 

 or by the bowel, or by transfusion of blood. The normal mode of relief of this 

 concentrated condition of the blood necessitates entrance of fluid into the body by 

 the mouth, and the feeling of dryness of the mouth which is relieved by fluid has 

 become part of an organised associative memory between concentrated blood and 

 the nervous centres in the bulb and cortex, which are connected with the sensori- 

 motor mechanism of the mouth, tongue, and throat. The same applies to the 



