Ixxviii INTRODUCTION 



investment, and the nervous fluid. The medullary pulp cor- 

 responds to the grey and white matter of the brain and 

 spinal cord, and the nervous tissue generally ; all he says 

 says about it is that it consists of an " albumino-gelatinous " 

 substance. The aponeurotic investment is, I suppose, the 

 pia mater. But the entire body of Lamarck's psychology is 

 based on the assumption of the existence of the third kind 

 of substance, namely the nervous fluid, which, as I have 

 already said, was electric fluid supposed to become modified 

 and " animalised " on entering into the bodies of the higher 

 animals. The main result of this animalisation is apparently 

 that, instead of being uncontainable, and free to permeate 

 the whole of the animal's body, it becomes containable ; 

 that is to say, there are certain tissues that it cannot traverse, 

 and the most important of such tissues is the aponeurotic 

 investment in which the entire medullary pulp is enclosed. 

 It can, however, still move rapidly within the medullary 

 pulp itself, without needing any visible channels. The 

 nervous fluid is thus encased within the aponeurotic invest- 

 ment of the nervous system : it precisely corresponds to the 

 " animal spirits " of the ancients. 



Lamarck held that in animals more primitive than insects 

 any nervous system which might exist had no other function 

 than that of exciting muscular movement. The system, he 

 imagined, then consisted of isolated ganglia, from which 

 nerves travelled to the muscles. He attributed the origin 

 of nerves to the expansive efforts of the nervous fluid within 

 the ganglia ; long nervous threads being thus thrust out by 

 the nervous fluid in its efforts to escape. In the insects 

 according to his view, the nervous system became sufficiently 

 integrated to endow the animal with feeling or sensation. 

 But it is not until we reach the lowest vertebrates, that is 

 to say, the fishes, that any kind of intellectual operation or 

 intelligent activity can be carried out. The existence of 

 sensation begins when the nervous system is united into one, 

 with a " main medullary mass " and a common nucleus 

 (foyer) for all the afferent nerves. The existence of intelli- 



