BOWMAN LECTUKE. LXVII 



by haemorrhage. Further, there can be little doubt that 

 in certain cases we have to deal with equivalent, substi- 

 tute, or heteromorphic diseases cases in which the same 

 cause produces disease of one part, e. g. the retina, in one 

 person and of another part, e. g. the organ of hearing, in 

 another member of the same genealogy. In popular no 

 less than medical belief such heteromorphisrn is sufficiently 

 notorious in the case of gout, though the evidence is some- 

 what lacking in precision. Lastly, can we regard it as 

 certain that single births, occurring at comparatively long 

 intervals, always follow the same laws of transmission as 

 frequently recurring multiple broods ? 



Amongst normal human characters the colour of the 

 iris has been investigated, and Hurst has shown that pig- 

 mentation is in Mendel ian terms dominant to lack of 

 pigment, i. e. the brown or otherwise pigmented iris is 

 dominant to the pure bine or grey iris. Captain Hurst* was 

 good enough to let me see, on May 17th last, at the Village 

 School at Burba ge, his home in Leicestershire, a consider- 

 able sample (thirty-eight) of the persons upon the colour of 

 whose irides his paper was based. I wished particularly to 

 know whether entire lack of visible pigment meant the 

 same thing to myself as to Mr. Hurst. Mr. Hurst's 

 method is to examine the iris with a magnifier out of doors 

 in good daylight. The ones I saw were all children 

 attending the school and we examined them in the open 

 'yard outside at about 2 o'clock. In those tliat ]\lr. Hurst 

 had recorded as " simplex/' i. e. entirely free from visible 

 strom a pigment, I could find not the least evidence of 

 pigment in any, except a doubtful slight trace at one part 

 of one iris in one child, so slight that I thought the 

 appearance might perhaps be due to the colour of an 

 unusually large blood-vessel. In the slightly and par- 

 tially pigmented ones Mr. Hurst's observations and mine 

 were also in complete agreement; in many of this class 

 the pigment, although very evident on careful scrutiny 



* Hurst, C. C,"The Inheritance of Eye-Colour in Man," Proc. Roy. 

 Soc , B., Ixxx, 1908. 



