130 JOHN BERRY HAYCRAFT ON 
very low organisation, Bacteria, Vibriones, and all organic ferments, a certain 
temperature is absolutely necessary to their development. 
As we pass up the invertebrate animal kingdom, we find in every class 
seasons of reproduction. In the vertebrata we have spawning seasons for the 
fishes ; amphibians, reptiles, birds, and mammals have all their breeding seasons. 
We might note here many curious zoological facts connected with the seasonal 
development of sexual organs, if the subject of the paper permitted. In the 
foregoing examples the temperature no doubt mainly operates through the 
vegetable world, varying the amount and quality of food at different times. 
Thus few animals breed in winter, when food is scarce and their bodily powers 
are at a low ebb. 
Amongst civilised men and domestic animals the variations in the amount 
of food are brought to a minimum, and as a consequence conceptions can occur 
all the year round, mostly, however, in summer. 
A dog can have pups in every season of the year; his food is ensured to 
him, and he is never reduced to extremes of hunger, as are his antecedents the 
wolf and the fox, who almost never have young in winter. 
Here we have an instance of how temperature influence can be ameliorated 
by more favourable circumstances, Amongst savage tribes of men, living in 
rigorous climes, the conception curve probably is more marked than in Scotland. 
We see therefore that temperature is a great—the greatest—factor modify- 
ing life. It modifies the number of children born ; it is connected, directly or 
indirectly, with almost every disease that is known; and therefore becomes a 
chief factor in producing the retrogressive change which we call death. 
In conclusion, I wish to express how much I am indebted to Professor Tarr, 
not only for having directed my attention to and explained to me the mode of 
applying Fourier’s formula to this investigation, but for having checked the 
results. Without his aid I could not have carried out the investigation. 
