8 THE CAVENDISH LECTURE 



That we may not single out any of our countrymen to be 

 pilloried to-night, I will give you a German instance which will 

 indicate what I mean. No problem can be more important than 

 the prevalency of syphilis in a large urban population ; a knowledge 

 on this point is one of the most urgent medico-social questions. 

 Well, how is it to be found out so long as syphilis is not notifiable? 

 Indirectly there are means of doing it. We know the deaths from 

 general paralysis of the insane, and there is one town in Europe 

 at least, namely Copenhagen, where syphilis is notified. It occurred 

 to Dr. Fritz Lenz that the ratio of deaths from general paralysis 

 to syphilitics notified, as found from Copenhagen, might be applied 

 to other towns. In other words he proceeded to deduce from the 

 known deaths per year from general paralysis in Berlin the number 

 of syphilitics that would be notified were notification there com- 

 pulsory. Armed now with the annual increase in the number of 

 syphilitics in Berlin, he found their total number by the simple 

 process of multiplying this annual increase by the expectation of 

 life at fifteen years of age ! The result was astounding ; practically 

 the whole population of Berlin is syphilitic ! Dr. Lenz did not 

 apparently find this result so improbable that he thought it worth 

 while to question his premises. Any actuary would have told him 

 that his problem could not be solved without a knowledge of the 

 age distributions of the populations in Copenhagen and in Berlin; 

 nor without regarding the fact that Berlin is a rapidly growing town 

 and Copenhagen is not. Further, Dr. Lenz should have realised 

 that the general age distribution of syphilitics is all important ; why 

 should the expectation of life of men of all ages, especially men 

 with syphilis, be thnt of boys at fifteen in the normal population, 

 the minimum age at which syphilis would be in the least likely to 

 be incurred ? 



Now here you have a capital illustration of a most important 

 medico-social problem, and you have a medical man with an 

 excellent key to its solution, but alas ! he is wholly wanting in the 

 training which would have taught him how to put it in the lock 

 and to turn it round. Gentlemen, this is only a single illustration 

 of the sort of problems which modern medicine has to deal with, 

 problems which crop up in almost every school report and in every 

 public health report, problems the solution of which .is essential 

 to social welfare, yet which cannot be solved without s[)ecial 

 training, and when the training is there, need a large staff of 

 practised computers working for months, if not years, to prepare 



