This, though a very efficient tonic under certain circumstances, must be considered as acting negatively. In large towns, the atmosphere is impregnated with effluvia, the general effect of which on the system is at first depressing, and ultimately debilitating. By removing from town into country, we escape this influence; and, the cause of weakness being removed, our systems acquire renewed strength through the healthful agency of an uncontaminated atmosphere. This is especially the case with invalids, whose strength has been impaired by disease, and whose systems are often unable duly to react, while exposed to the air of cities. I presume there are few inhabitants of large towns who have not felt, even in their ordinary health, the refreshing and invigorating effect of the country atmosphere, or, to speak more accurately, of an escape from the enfeebling effluvia to which they are habitually exposed.

The sick chamber is liable, in a still greater degree than the general atmosphere of towns, to the charge of unwholesomeness; and, even in the country, therefore, invalids are often greatly benefited by escaping from the confined and sedative air of their lodgings to that of the open fields.

These remarks, while applicable to debility in general, are peculiarly so to that of convalescence.

But, though pure air may be only negatively tonic at the ordinary atmospheric pressure, yet, by exposure to the atmosphere either much rarified or much condensed, a tonic influence on the respiratory organs is obtained, in the former case indirectly, in the latter directly, from which much good may be expected in debilitated conditions of those organs.*

* From observations by Dr. Hermann Weber on the climatic influence of the high regions of the Swiss Alps, he came to the following conclusions.

Respiration is increased in frequency and depth, with increasing elevation.

The heart contracts more frequently in proportion to the height attained.

The appetite, and generally thirst, are augmented.

Sanguification is improved.

The nervous system is invigorated, and the sleep more healthy.

The muscular system acquires increased energy, and is more active.

It is inferred that the metamorphosis of tissue is augmented; though the urine does not appear to be materially altered in quantity; the proportion of solids being only probably somewhat increased. (Dublin Quart. J. of Med. Sci., Feb. 1, 1864, P. 42).