I.—PHYSIOLOGY. 225 
present rationalisation of the effects observed. It can hardly be doubted 
that they will potently influence the methods by which, in the immediate 
_ future, new and still better specific remedies are sought. But though our 
_ practical aim, in relation to the affinities of a remedy for the parasite and 
for the host’s tissues, may be radically changed, the meaning of these 
specific affinities, so delicately adjusted to a precise molecular pattern, 
remains dark. Ehrlich’s chemoreceptors may no longer satisfy us, but 
_ we have nothing equally definite to replace them. I have endeavoured 
to indicate what seem to me hopeful signs of new contacts between bio- 
_ chemistry and chemotherapy. There is promise, in another direction, 
] that at least some aspects of the problem of immune specificity are being 
_ brought within the scope of strictly chemical investigation, as in the recent 
work of Avery and Heidelberger, on the constituent of a pnheumococcus 
_ which combines with the specific precipitin. As in Ehrlich’s pioneer work 
_ in chemotherapy, it can hardly be doubted that an increased under- 
standing of the meaning of immune specificity, which but a short while 
ago might have seemed hopelessly beyond the range of attack by chemical 
weapons, will still influence ideas, and help to shape the course of further 
investigations, on the chemotherapeutic process. As the biological com- 
plexity of the problem is realised, it becomes increasingly a matter for wonder 
_ and admiration that so much of practical value has already been achieved 
—the treatment of the spirochetal infections, syphilis, yaws and relapsing 
fever, revolutionised; Leishmania infections, kala-azar and Baghdad 
boil, and Bilharzia infections, which crippled the health of whole populations 
in countries such as Egypt,now made definitely curable; trypanosome infec- 
_ tions, such as the deadly African sleeping-sickness, after years of alternating 
_ promise and disappointment, brought now at last within the range of 
effective treatment. And if such results have already been attained, in 
a period during which practice has often and inevitably outrun theory, 
we may well be hopeful for a future in which fuller understanding should 
make for more orderly progress. 
“1924 Q 
