Kerslake Curette Sir,-the Letter From

endocrine hypothesis. For example, there must be in the population many men who have regularly donated blood every six months for many years. Obviously this is not equivalent to a monthly menstrual bleed. Nevertheless it would be interesting to see whether these men are in any way protected against coronary thrombosis as compared with a group of non-donors. (2) If true the concept would mean that protection against coronary thrombosis could be provided at very low cost. There would be no need for life-long drug taking or dietary changes. (3) If the bleeding hypothesis were true, the blood transfusion service would cease to have any problem in acquiring blood. I realize that my hypothesis is very unlikely to be valid. But when so little progress is being made in other directions and when the potential rewards are so great, a survey of the effects of blood donation on coronary disease would appear to be worthwhile.-I am, etc., NAFISA HORROBIN.