112 CHEMICAL COMPONENTS OF THE HUMAN BODY. 



soluble compound, that we are to attribute the good effects which have been 

 obtained from the use of iodide of potassium in removing Lead from the system. 



7. General Summary. Operation of Chemical Forces in the Living Body. 



90. We have now passed in review the chief among those components of the 

 Human body whether presenting themselves in its nutritive fluids, in its solid 

 tissues, or in its excretory products whose existence has been made definitely 

 known by Chemists. It is by no means to be assumed that what has here been 

 stated affords a complete list of the chemical components of this fabric; still 

 less, that the account which has been given of the metamorphoses they undergo, 

 is to be received in the light of a determinate scheme. We should, indeed, regard 

 it as a mere sketch or outline, in which the broad features are conveyed with 

 tolerable distinctness, but of which the details remain to be filled in by careful 

 study. And the greatest advantage which can be derived from this method of 

 viewing the subject, consists in the more definite boundary we are enabled to 

 draw between what is known and what is unknown, and again, between what 

 rests on a fair basis of probability, and what has no better foundation than vague 

 surmise. Moreover, there is an obvious advantage in combining the chemical 

 and the physiological view of the facts in question. For the mere Chemist will 

 not only be liable to continual error, when he attempts to reason as to what 

 takes place in the penetralia of the living body from what he observes in his 

 laboratory, without taking into account the difference in the conditions of the 

 phenomena (of which kind of error some of the speculations of Prof. Liebig have 

 afforded remarkable examples) ; but he will also be at a great disadvantage in 

 the prosecution of his inquiries, for want of the guiding clue which Physiologi- 

 cal knowledge alone can afford. On the other hand, the Physiologist cannot 

 safely make a step in advance, when engaged in the study of the metamorphoses 

 of the alimentary materials into the living solids, and of the subsequent reduc- 



- tion of the latter to the condition of excrementitious matters, without relying 

 on those exact data which Chemical tests and analyses can alone supply ; it 

 being to these, in fact, that he owes whatever definite knowledge he possesses 

 of the composition of these several bodies, with which it is of -the most funda- 

 mental importance that he should be acquainted. Accordingly, all the most 

 productive researches of recent times, in this department, have been the work 

 of men, who have either combined within themselves these two kinds of know- 

 ledge, or who have brought them to bear upon one another from extraneous 

 sources. 



91. The following Summary is intended to convey, within a narrow compass, 

 the leading conclusions, in regard to the Chemistry of the living Body, to which 

 the Chemico-physiological labors of recent times appear to point. 



I. The organic materials indispensable for the genesis of Tissue, consist of 

 Albuminous and Fatty compounds. The former present themselves under various 

 aspects, in the Vegetable as well as in the Animal kingdom, all being reducible, 

 however, to the ordinary state of Albumen by the digestive process ; and in 

 their natural states of combination, they include most of the inorganic substances 

 which are required in addition. There is no reason whatever to believe, that 

 Albuminous compounds can be generated within the animal body, by the trans- 

 formation of substances belonging to an entirely different type. The latter are 

 directly afforded by ordinary animal food, and by many kinds of vegetable pro- 

 ductions ; and it seems to be when they are thus supplied, that they are most 

 readily made available in histogenesis. They may be produced within the body, 

 however, by the metamorphosis of either Albuminous or Saccharine compounds. 



II. The great mass of those tissues of the body which belong to the cellular 

 type, is generated at the expense of Albuminous matter ; fat-particles, however, 



