Comparative Physiology, 391 



say whether it was a change of indusiums or pictures. Tlie 

 training of standard fruit trees in the form of inverted umbrellas, 

 &c., is surely an improper violation of natural developement. 



In Chap. IV., On the general View of the Functions of ani- 

 mated Beings, and their mutual Relations. " In order to arrive 

 at any certain general conclusions, the physiologist must collect 

 and compai'e all the facts of similar character which the study of 

 animated creation furnishes. From the simple cellular plants 

 we should obtain very vague ideas of the character of the 

 nutritive processes, as we cannot separate them, and investigate 

 them apart ; and, on the other hand, we should form very 

 erroneous ideas of the essential conditions of these processes, to 

 study them only in their most comj)lex form and specialised 

 condition. It is only from a comprehensive survey of the whole 

 organised creation, embracing each extremity of the scale, that 

 laws possessing a claim to general application can be deduced. 

 The essential part of the function of respiration is, the aeration 

 of the blood by an interchange of ingredients between the cir- 

 culating fluid and the air, from the exposure to the atmosphere, 

 or to water holding air diffused. The alterations in the ca- 

 pacity of the chest, which are effected by the actions of the 

 diaphragm and external muscles, only serve to reneAv the quan- 

 tity of air in contact with the membrane of the lungs which 

 expose the blood to it. They have no share in the aeration of 

 the blood, excej)t by supplying its conditions. If these could 

 be supplied independently of them, the essential part of the 

 function would be performed as well as with them. In all of 

 the functions, some of the changes are essential, and some super- 

 added. Keptiles, having no diaphragm, fill the lungs by a 

 process resembling swallowing. In fishes the blood is sent to 

 meet the water, Avhich is in apposition with the external sur- 

 face. In the lower animals a change of water is supplied by 

 their moving from place to place ; or, when fixed to a particular 

 spot, by means they possess of creating currents, or vortices, by 

 cilite, to draw to them a supply of food. In plants the essen- 

 tial part of the function is performed without any movement 

 Avhatever, the wide extension of the surface in contact with 

 the atmosphere affording all the requisite facility for the aera- 

 tion of the circulating fluid. 



" In all living beings, the appi"opriation of alimentary ma- 

 terials from Avithout, their conversion into a nutritious fluid 

 to supply materials for the growth and renovation of the fabric, 

 and the excretion of unfit particles, constitute the sum of the 

 vital acts by which the individual is supported. The main- 

 tenance of individual life, however, is not all that is required ; 

 all organised structures must be produced by others previously 

 existing, no living being ever taking its origin in spontaneous 



