DOUBLEDAY'S THEORY 181 



different species. They find that if a small quantity of 

 some alkali, such as sodium hydroxide, be added to the 

 sea-water in which certain species live, the degree of 

 fertilisability is so raised that even widely separated 

 marine species can fertilise each other. Sea-urchins and 

 starfish, or even sea-urchins and molluscs can be crossed, 

 and will produce hybrids which transmit the character 

 of the female. With the aid of an alkali, salt, or sugar, 

 it is also possible to secure artificial parthenogenesis in 

 species whose normal mode of reproduction is sexual, 

 and the resulting larvae develop normally and live as 

 long as the offspring from fertilised eggs. The facts in 

 regard to alkali certainly provide astonishing confirmation 

 of a hypothesis published eighty years ago. 



Doubleday also suggested that " the neutralisation or 

 absence of alkali in the male animal constitution would 

 be a direct cause of sterility, and its decided presence, 

 e contrario, a cause of fruitfulness, supposing in such 

 case the female to be prolific by constitution." He then 

 pointed out that the tendency of a plethoric diet is to 

 produce an abundance of acid in the body, as seen in 

 cases of gout, and that the tendency of too poor and 

 scanty a diet is to develop an alkalescent state, as seen 

 in scurvy, a disease produced by deficient and unwhole- 

 some diet. It is well established that acid is fatal to the 

 germ cells, perhaps through neutralising the alkali, but 

 an excess of alkali seems to be equally fatal. Probably 

 there is an optimum point for this as for other factors. 



This work of Thomas Doubleday was a most valuable 

 contribution to the study of the problem of the birthrate 

 and the laws which govern fertility. But, as not in- 

 frequently happens, he was completely baffled by the 

 blindness of his contemporaries. They were infatuated 

 by the theory of Malthus, who had provided them with 

 an admirable excuse for their selfishness, and were most 



