I885.J 
Testing for Colour-blindness. 
409 
same sex are produced, thus restoring the balance. Want 
of nutriment has the same effeCt as sexual overwork. Weak 
bulls with powerful cows produce chiefly bull-calves ; weak 
cows with strong bulls drop more cow-calves. 
As for age, each individual at the time of its greatest 
sexual capacity is least disposed to impart its own sex to its 
descendants. In the human species the excess of boys is 
therefore greatest when the husband is considerably older 
than the wife. Dtising is therefore of opinion that ani- 
mals have acquired the power of adaptation to produce 
more individuals of the sex which is in a temporary mi- 
nority. 
When food is present in abundance more females are 
born ; in times of scarcity more males, because the chief 
burden of reproduction devolves upon the female. 
Diising draws the following conclusions from observations 
on the lower animals : the sexual proportion is self-regu- 
lating. That sex is produced more abundantly whose 
increase is at the time being the more advantageous for the 
preservation of the species. Such conclusions are not to be 
accepted without caution. 
VII. TESTING FOR COLOUR-BLINDNESS 
IN THE MERCANTILE MARINE. 
By Jabez Hogg, M.R.C.S., F.R.M.S., &c., 
Consulting Surgeon to the Royal Westminster Ophthalmic 
Hospital. 
J ' N a former paper, “ Homer Colour-blind,” I very slightly 
touched upon the wider question, — one which pos- 
sesses interest for most people, — colour-blindness, as 
affecting mankind in general and the mercantile marine in 
particular. Although the investigation of this remarkable 
phenomenon brought to light a curious facft, that on an 
average one male out of every twenty-five is quite unable to 
discriminate the principal colours of the speftrum, it ex- 
cited no great deal of attention until it became apparent 
that, both on our iron-roadways and on the ocean, deplorable 
accidents were likely to — and often did -occur, from the 
VOL. VII. (THIRD SERIES). 2 F 
