Dr. Mac CuUoch on Malaria on Ship'board. 49 



ever is proved in those sciences which do not admit of mathe- 

 matical demonstration. 



I may divide the imaginary causes which physic has assigned 

 into two classes ; — those which depend on man himself, includ- 

 ing injurious diet, fatigue, the passions,' and so forth, are 

 equally distributed, on a broad average, throughout mankind, 

 everywhere, and at all seasons of the year, or in all climates. 

 As to injurious conditions of temperature and of moisture, 

 they are not amenable to the same universal average ; but 

 they occur also under certain distinct sets of averages, entirely 

 different from those which attend the existence and action of 

 malaria. 



Now, if what I have termed human causes were the causes 

 of non-contagious fever, that should occur indiscriminately, and 

 on some equable general average, all over the world. That, 

 admittedly, is not the fact ; and I may surely, therefore, safely 

 dismiss them from the list of causes which physic has registered. 

 There is nothing wanting, even to demonstration, as to this 

 branch of these supposed causes. 



The second division of causes, consisting in modes of tem- 

 perature, cannot be dismissed so briefly ; because physic, with 

 its usual laxity of language, has even enumerated all the cir- 

 cumstances, without the requisite discrimination. If they 

 were really causes of fever, it is difficult to see how any one 

 should escape ; or, rather, there would be found a certain 

 average, or certain averages, of fevers equably spread over 

 certain average climates all over the world, which is not the 

 fact. I must make the discrimination here, for physic, which 

 it has not itself done. 



The operations of temperature must consist in certain states, 

 or changes, which can be defined. It may be continuous 

 cold, or a mean heat, which we may, perhaps, safely take 

 about 40'' (I need not be accurate here) ; or it may be conti- 

 nuous heat, which, in a similar loose way, may be taken at 65°; 

 or it may consist in sudden transitions from cold to heat, or 

 the reverse. It is generally esteemed that the effect of mois- 

 ture is dependent on temperature, or is a mode of the action 

 of that cause : should it be thought otherwise, it may be dis- 

 tinguished into excess or defect. Such is a more accurate 



JULY — SEPT. 1828. E 



