456 



SCIENCE. 



[Vol. I., No. 16. 



motion as is possible for a molecule of a solid reaches 

 a maximum value which can only decrease, whether 

 the amplitude of the oscillation be increased or dimin- 

 ished, and that the only way in which it is possible 

 to increase the mean kinetic energy of this Ivind of 

 motion is to impart sufBcient additional energy to 

 change the motion into one of complete rotation. By 

 such a process, greater freedom of motion is given to 

 the molecules, and a large amount of energy becomes 

 potential. This is regarded as explaining the phe- 

 nomenon of liquefaction. 



It is shown by an extended mathematical discus- 

 sion of the cohesive forces and resistance to compres- 

 sion, by which molecules hold each other at mean 

 fixed distances, that the mean kinetic energy of the 

 vibration of molecules about their mean positions also 

 has a maximum value which can only be increased 

 by removing them to such mutual distances that the 

 cohesive forces no longer act. In this process a large 

 amount of energy also becomes potential. This is 

 regarded as the rationale of the phenomenon of 

 vaporization. 



It is further shown, that, on this theory, it might 

 very readily occur that the specific heat of a liquid 

 should at first decrease, and then increase, as Rowland 

 has proved is the case with water, but that the spe- 

 cific heat could not at last decrease. 



The cause of the relatively large specific heat of 

 most liquids is treated. It is shown that the distri- 

 bution of rotary velocities in free rotation, such as the 

 molecules of a liquid are supposed on this theory to 

 have, is such that the atoms of some small per cent 

 of the molecules in any given mass must be torn 

 asunder. What per cent of the liquid may be thus 

 dissociated will depend upon the temperature and 

 constitution of the liquid; it being smaller for the 

 simpler liquids, and increasing with the temperature. 

 Electrolysis is an evidence of this action. Such dis- 

 sociation sufficiently accounts for the generally high 

 specific heats of liquids. 



There is a general qualitative accordance of the 

 theory with observed specific heats. A further con- 

 firmation of the theory is found in the clear ex- 

 planation it affords of the existence of a critical 

 temperature, above which a vapor is uncotidensable 

 by pressure alone; for, when the mean kinetic. energy 

 of all the molecules of a liquid acquires a value greater 

 than the maximum possible in a liquid state, the 

 liquid is not only vaporized, but necessarily becomes 

 an uncoudensable gas, and remains so. 



GERMS AND EPIDEMICS.^ 

 After a brief historical sketch showing the idea 

 that certain diseases, and especially marsh-fevers and 

 the plague, are caused by the entrance of minute liv- 

 ing organisms into the body, to be a very old one, but 

 one which, until within a few years, has had no ex- 

 perimental proof, some definitions were given of the 

 terms now used in discussion of this subject; and the 

 word ' microdeme,' meaning ' little living thing,' was 

 proposed as a general designation for the minute liv- 

 ing particles found in almost all air or water. The 

 microdemes include the Microphytes, or minute vege- 

 table organisms, and the Microzoa, — the microzomes, 

 the bacteria, microbia, micrococci, etc. There is at 

 present no evidence that any microdemes are derived 

 from any source other than other living organisms, 

 nor that the special microphytes which cause the vari- 

 ous processes known as fermentations or putrefac- 

 1 Abstract of a lecture by Dr. J. S. Billings, given in tbe 

 Saturday course at the U. S. national museum, Washington, 

 Feb. 17. 



tions ever develop into the higher forms of fungi; 

 although this Is still an unsettled question, and there 

 is some reason to think that some of the higher fungi 

 may act as ferments. 



The prevailing opinion at present is, that there are 

 many different kinds of microphytes, each having 

 special powers, and that each can only .propagate its 

 own kind within a certain limited time. 



But it is also probable, that by changes in nutriment, 

 temperature, etc., changes in their habits and powers 

 may be produced through natural selection. These 

 changes are so considerable as to cause them to ap- 

 pear to be new species. The germ theory is, that cer- 

 tain diseases are due to the presence and propagation 

 in the system of minute organisms which have no 

 part in its natural economy. The word 'germ,' how- 

 ever, is often erroneously applied to independent 

 organisms which originate outside of the body itself, 

 such as the particles in vaccine lymph which are not 

 microphytes, and can hardly be called independent 

 organisms. 



The diseases caused by large and comparatively 

 well-known organisms are called parasitic. Such are 

 some varieties of skin-disease ; as ring-worm, or the 

 so-called live spots, the fungus foot of India, and the 

 disease of the ear due to the growth of a peculiar As- 

 pergillus. A new disease of this kind is the so-called 

 actinomycosis, due to a fungus which forms tumors 

 near the angle of the jaw, and which causes death 

 when it becomes generalized. 



An account was then given of the organisms found 

 in splenic-fever, relapsing-fever, chicken-cholera, lep- 

 rosy, etc., and the method of Pasteur for the so-called 

 attenuation of virus was described. This method 

 appears to depend largely on the exposure of the 

 broods of micro-organisms to the influence of oxygen; 

 and recently MM. Nocard and Mollereau have an- 

 nounced that the same can be effected much more 

 rapidly by the use of oxygenated water. The ques- 

 tion as to whether Pasteur's inoculation with artifi- 

 cially modified virus will afford permanent protection 

 is still unsettled, for sufiicient time has not elapsed 

 to decide it; but there is reason to hope that it will 

 be found to be of great practical benefit. 



The effects of microdemes in producing pyaemia 

 and puerperal-fever are well described, and attributed 

 to a poison secreted by them, of the nature of the so- 

 called ptomaines, rather than to their mere mechani- 

 cal presence. This knowledge is practically applied 

 in what is called antiseptic surgery; and the sur- 

 geon now undertakes, without hesitation, operations 

 which, twenty years ago, would have been deemed 

 quite unjustifiable; for he knows, that by insuring 

 that neither through the air nor the water, the sponges 

 nor the instruments, nor in any other way, a single mi- 

 crodeme which has not had Its powers of growth and 

 reproduction totally destroyed shall gain admission to 

 the wound, he need have no fear of blood-poisoning. 



As regards diphtheria, it is probable that it is due 

 to a common micro-organism, which, under circum- 

 stances not yet understood, becomes virulent, as the 

 micro-organisms of common sweet-hay infusion may 

 be transformed into those which cause malignant 

 pustule. 



The connection of consumption with a microphyte 

 is still doubtful, though not improbable; and the 

 same may be said with regard to malaria. 



A sketch was then given of some of the character- 

 istic phenomena attending the great epidemics. For 

 some, the germ theory appears to afford the best 

 explanation; for others, such as influenza or cerebro- 

 spinal fever, this theory is quite inadequate. 



Special attention was called to the many points in 



J 



