36 



taken to guard against the vicissitudes which frequently occur at that 

 season. Animals brought from warm climates to those which are 

 colder suffer under the same evils as animals exposed in summer to 

 a considerable reduction of temperature. Tropical animals should 

 therefore on their first importation be placed in apartments of higher 

 temperature, which may be gradually reduced to that usually main- 

 tained in the part of the menagerie appropriated to similar animals. 



The state of the atmosphere as regards humidity and dryness is of 

 the highest importance to health. A very humid atmosphere does 

 not exist at a temperature much below 40°, for when there is any 

 great degree of frost the moisture is precipitated -, but a temperature 

 of 40° when the air is saturated with damp is highly injurious, pro- 

 ducing catarrhs and coughs, which are frequently cured by a sharp 

 frost. Our insular situation may expose us especially to humidity, 

 which has a bad effect, on vegetation at least, by intercepting light. 

 The degree of luminousness in the atmosphere is probably of more 

 importance in climate than is generally imagined. Between Havre 

 de Grace and Portsmouth it is but eleven hours sail, yet there is 

 evidently the difference of a complete climate in the productions of 

 the soil and in animal life 5 the pomegranate and the vine grow- 

 ing in the former place with luxuriance and fertility, and many in- 

 sects which are here scarce, occurring there in the utmost profusion. 

 The cold and humid atmosphere prevalent during our winters, and 

 commonly called raw cold, is highly prejudicial to animals ; and its 

 evil effects are so much the more rapidly produced, as by the de- 

 position of the moisture on the covering of the animal, the wetted 

 fur or wool (as occurred in an experiment made by John Hunter on 

 the freezing of a Dormouse) is changed from the state of a bad to that 

 of a good conductor of heat. During the continuance of such a state 

 of atmosphere the apartments of the animals should be kept closed, 

 and only so far opened as may be necessary for ventilation. Much 

 of the humidity might be abstracted from the air by means of lime, or 

 perhaps still more effectually, as suggested by Leslie, by dry vegetable 

 mould. 



Extreme dryness of the atmosphere combined with cold is equally 

 prejudicial, as was proved by M. Edwards, with the combination of 

 cold and moisture j the latter causing mischief by the degree of cold 

 it produced, and the former by the increased transpiration which it 

 excited from the mucous surfaces. During March and April espe- 

 cially this dry and cold state of the atmosphere prevails in England 

 with winds from the N. and N.E. j and Mr. Daniell states that he 

 has seen the dew point of his hygrometer at 20° to 30° below the 

 temperature of the atmosphere, evidencing a degree of dryness 

 scarcely surpassed by that of the Harmattan. This state of atmo- 

 sphere is almost diametrically opposed to that of tropical climates 

 generally ; a remarkable instance of which is afforded by the obser- 

 vations of Captain Sabine in Africa, where the dew point was almost 

 at full saturation. It must consequently, though highly injurious to 

 all animals, be more particularly so to those brought from tropical 

 regions. Its effect is to produce inflammation of the mucous surfaces, 



