THE SCAVENGERS OF THE BODY. 379 



times the lake dried up, and again it has overflowed and inundated 

 the low lands in the neighborhood, as in 1827 and 1862. Often 

 its water has been set boiling by escaping gases. It would be in- 

 teresting to know what varying pressure caused the changes in the 

 level of this lake on the top of Mount Catarman. 



A further idea of the volcanic activity of this region may be 

 gained from the circumstance that a volcanic island emerged from 

 the sea on the north coast of Luzon in 1856, which grew to seven 

 hundred feet in height by 1860, and is now about eight hundred 

 feet high. Every one has seen photographs of the streets of Ma- 

 nila after an earthquake, which form of subterranean activity is 

 so common that it is taken into account in building. 



THE SCAVENGEES OF THE BODY. 

 Bt m. a. dastre. 



THE labors of M. Metchnikoff have made known one of the 

 most curious mechanisms — perhaps the most effective — which 

 Nature employs to protect the organism against the invasion and 

 ravages of microbes. We are only beginning to learn the means 

 which are provided for our defense against the countless swarms 

 of enemies of this class, some of them exceedingly dangerous, 

 among which we have to live and move. In the first rank of these 

 defenses is phagocytosis. The struggle of the organism against its 

 minute assailants is an image of human wars. The cutaneous or 

 mucous integument, continuous over the whole body, constitutes a 

 kind of fortified inclosure which the microbe can not penetrate, ex- 

 cept where some breach has been made. On one side of that wall, 

 in the living city, the phagocytes or leucocytes (white cells) form 

 an immense defensive army in a state of continual mobilization, or, 

 as M. Duclaux would say, an innumerable and vigilant police. 



These phagocytes or leucocytes are the nomadic elements of our 

 economy. The animal body may be compared to an organized 

 city in which all the living corpuscles, all the cellular elements, are 

 sedentary, each having its place and staying there. Hence the 

 comparison, often made, with the stones of a building, which is not 

 exact, however, because these vital elements grow and increase, 

 enlarging the structure without change of arrangement, while the 

 stones do not. The growth and nutrition of these anatomical ele- 

 ments, it should be added, are carried on exclusively at the expense 

 of liquid matters. IN'othing solid can enter them or come out 

 from them. 



