THE PREVENTION OF MALARIA 493 



of other Protozoal infections, that the infectivity of the mosquito 

 persists a long time, when once acquired ; that is to say, that a 

 mosquito which can infect at its fourth meal can do so also at its 

 fifth, sixth, ... or ;^th feed, probably for some months. It seems 

 clear, therefore, that the biting factor requires a much more 

 complex mode of expression than that given to it by Ross. 



The method of mathematical exposition is developed by 

 the author in an interesting manner through many formulae 

 and equations. For instance, if m be the proportion of 

 infected persons at the beginning of an anti-malarial campaign, 

 and ;/^i the proportion at the end of a given period, then 



Jill = m + b-sai{i - in) m - rin, 



where r denotes the average proportion of infected persons 

 who recover during a given period. That is to say, the 

 number of persons infected with malaria at the end of a 

 given period will equal those at the beginning, plus the number 

 of new infections, and minus the number of recoveries. This 

 is a very important consideration, since it shows that if, as the 

 result of anti-malarial measures, the new infections are less in 

 number than the recoveries, the disease must disappear inevit- 

 ably, in course of time, if the preventive measures are continued 

 persistently. Ross suggests that the malaria formerly prevalent 

 in some parts of England has died out gradually in this manner. 

 We doubt if this method of treatment will make malarial 

 problems any clearer to the ordinary person who is unaccus- 

 tomed to express his thoughts in mathematical formulae. The 

 most that can be said for it, from the purely practical point of 

 view, is that the symbols b, s, a, t, r, form a useful menioria 

 tcchnica, by means of which to keep in mind the various factors 

 upon which the prevalence of malaria depends in a given 

 locality. The formulae themselves tend rather to produce per- 

 plexity, especially when printed inaccurately, as on p. 254, lines 

 II and 12, where it is clear either that m and nti have been inter- 

 changed, or that " less " should be " greater " and " reduced " 

 should be " increased." Whilst on the subject of misprints, it is 

 to be regretted that the book does not show evidence of very 

 careful proof-reading, especially as regards proper names. The 

 honoured name of Leuckart is spelt wrongly on every one 

 of the numerous occasions on which it is cited, and we note 

 Giolgi for Golgi (p. 6"/) and Ostler for Osier (p. 646). 



