Public Parks. 33 



"a comparison," says Bain, "that transfixes the mind with the idea 

 of observing, recording, and explaining the facts of the world." 



This definition I shall apply to sanitary science, in connection 

 with public parks, and, as best I can, explain general laws and draw 

 deductions from the facts within my reach, with regard to the climate, 

 topography, and diseases of this locrdity. Although some of the 

 facts collected during 1866, and the f^rst half of 1867, are not as full 

 nor as accurate as those collected since, still they are sufficiently so 

 to indicate the general laws governing and controlling them. 



VEGETABLE PHYSIOLOGY. 



In order to appreciate the important part that the vegetable 

 kingdom performs in the economy of nature, and particularly its 

 effects upon animal life, it will be necessary to call attention to the 

 elementary composition of plants, the nature of the food by which 

 they are nourished, the sources from which this food is derived, and 

 the transformation it undergoes in their system. In the process of 

 digestion or assimilation is found the nature of vegetation, as in this 

 process alone mineral and unorganized matter is converted into the 

 tissues of plants and other forms of organized matter, the vege- 

 table kingdom occupying a position between the mineral and the 

 animal kingdoms. In living bodies there is a state of internal 

 activity and unceasing change — particles which have served their turn 

 being continually thrown out of the system as new ones are brought 

 in, thus constantly undergoing decomposition and recomposition. 

 Plants are organized beings that live directly upon the mineral king- 

 dom — and upon the surrounding earth and air, and, as a necessary 

 result of assimilating their organic food,they decompose carbonic acid, 

 and restore its oxygen to the atmosphere. Animals in respiration, 

 continually recompose carbonic acid at the expense of the oxygen of 

 the atmosphere and the carbon of plants. Plants absorb their food 

 entirely in a liquid or gaseous form, by imbibition, according to the 

 law of endosmosis, through the walls of the cells that form the 

 surface — as when liquids of unequal density are separated by a 

 permeable membrane, the lighter liquid or the weaker solution will 

 flow into the denser or stronger with a force proportioned to tlae 

 difference in density ; but at the same time a smaller portion of the 

 denser liquid will flow out into the weaker, which process is called 

 exosmosis. 



