106 Mr. T. Hopkins's Observations on Malaria. 



afterwards attempts to show that heat and moisture are merely 

 agents in the production and distribution of a poisonous ex- 

 halation from vegetable matter, which exhalation he says is 

 the true malaria. A moist air, says he, " is the best con- 

 ductor of the malaria, as moisture in the air, under the form 

 of evening mists or in other modes, appears to be even its 

 proper vehicle or residence." And again he says, " water 

 in some form is necessary to the production of that peculiar 

 vegetable decomposition which is the source of this poison ; 

 and the action of moisture is twofold, inasmuch as it not 

 only accelerates vegetable decomposition, but renders the at- 

 mosphere a fitter conductor of the poison." It is not here 

 pretended that this poison which is stated to be the result of 

 vegetable decomposition has ever been detected in a palpable 

 form. It is not asserted that its existence as a peculiar sub- 

 stance has been ascertained. It is only from effects produced 

 on human health that its existence is inferred. Moisture, says 

 the Doctor, is not capable of poisoning the atmosphere ; and 

 as he finds that the atmosphere is poisoned, he infers that 

 the poison is exhaled in the decomposition of vegetable sub- 

 stances. 



There is a prevalent belief in many parts of the world that 

 fogs coming from the sea produce feveis of the same kind as 

 the malaria fever : this belief is evidently at variance with the 

 theory espoused by Dr. Macculloch, and he thus reasons with 

 those who entertain it. " The proof that it is malaria in the 

 fog, and not the fog itself which is the cause of disease, is 

 evinced by the following facts : No intermittents are ever 

 produced on the western or northern shores of the island, and 

 for the plain reason that there is no land whence they may 

 arrive. The clouds of mountainous regions do not produce 

 fevers though these are also fogs; and what forms a most ab- 

 solute proof of this is, that in Flanders it is the fogs which 

 come with a south-west wind or the southerly winds which 

 transport and propagate malaria and diseases, while as soon 

 as the winds shift and blow from the sea the fevers disappear, 

 though these particular winds are so charged with fog as to 

 darken the whole country for days," These are the facts on 

 which the Doctor relies, and he remarks, that " it ought 

 surely to be unnecessary to say that if fogs alone could pro- 

 duce such fever water itself must be the poison, since a fog is 

 a cloud, and its constituents when pui'e are only atmospheric 

 air and water." 



With respect to the first alleged fact, that no intermittents 

 are produced on the western or northern shores of our island, 

 the reason for it may be found in the circumstances of these 



