176 LIFE: ITS NATURE AND ORIGIN 



A great variety of specific molecules and other particulate units 

 are carried throughout every biont by diffusion, convection and 

 circulation. In the course of time each cell, including the 

 gametes, will receive whatever of this molecular flotsam and jetsam 

 can enter into and endure in its cytoplasm, or else establish there 

 specific catalyst surfaces, so that among these entering molecular 

 or near-molecular units would be those that determine, or assist 

 in determining, differentiation. Apart from other evidence, the 

 fact that some differentiated cells have been found to breed true 

 in tissue cultures warrants the belief that specific tissues or organs 

 contribute to the molecular melee in the organism units capable 

 of determining the formation of their own specific type of cell. 

 On the other hand, de-differentiation may occur: heart cells tend 

 to breed true as heart cells, cancer cells as cancer cells, etc. 



Since excessive use of a part or of an organ commonly leads to 

 its hypertrophy, this would tend to increase the total quantity of 

 hypothetical modifier substances emanating from such part or 

 organ, and would increase its equilibrium amount in the gametes. 

 This is a hypothetical physicochemical mechanism which might 

 in some cases lead to the inheritance of acquired characteristics 

 based on the use or disuse of parts. 



Without suggesting a mechanism for their action, J. T. Cunning- 

 ham 22 advanced a Lamarckian view involving hormones as active 

 factors in heredity. He pointed out that special glands are not essen- 

 tial for the production of these internal secretions; for his colleagues 

 at the University of London, W. M. Bayliss and E. H. Starling, had 

 shown in 1902 that the wall of the intestine produces the hormone 

 secretin which, carried by the blood, activates the pancreas to secrete. 

 Cunningham stated: "There is nothing improbable in supposing that 

 a tissue stimulated to excessive growth by external irritation would 

 give off special substances to the blood. We know that living tissues 

 give off waste products, and that these are not merely pure C0 2 

 and H 2 0, but complicated compounds. The theory proposed by me 

 in 1908 was that we have within the gonads numerous gametocytes 

 whose chromosomes contain factors corresponding to different parts 

 of the soma, and that these factors or determinants might be stimulated 

 by waste products circulating in the blood and derived from the parts 

 of the soma corresponding to them. There is no reason to suppose 

 that an exotosis formed on the frontal bone as a result of repeated 

 mechanical stimulation due to the butting of stags would give off a 

 special hormone which was never formed in the body before, but it 

 would probably in its increased growth give off an increased quantity 



