October 5, 1888.] 



SCIENCE. 



163 



Only the following- animals have corpuscles larger than man, i.e., 

 larger than ;^\„ of an inch; viz., the elephant, great ant-eater, 

 walrus, sloth, platypus, whale, capibara, and (according to Worm- 

 ley) opossum. Animals the corpuscles of which are slightly below 



man in size, i.e„ having corpuscles from j^'oj to 



of an inch 



average diameter, are the seal, beaver, musk-rat, porcupine, mon- 

 key, kangaroo, wolf, and guinea-pig. None of these are domestic 

 animals. All other animals, including all domestic animals, have 

 blood-corpuscles of a mean diameter less than tjeVtt of an inch; 

 and, in fact, those animals which, as a rule, are blamed for blood- 

 stains found on the clothing and apparel of criminals (ox, pig, horse, 

 sheep, and goat), have corpuscles with an average diameter less 



than 



of an inch. He summarizes the facts as follows : - 



1. The blood-cor|)uscles of birds, fishes, and reptiles, being oval 

 antl nucleated, can never be mistaken for human blood. 



2. Fresh human blood cannot be mistaken, under the micro- 

 scope, for the blood of any animal the corpuscles of which have a 



mean diameter of less than 



or even jiVu' °f 'in inch. 



3. (a) If the average diameter of blood-corpuscles in fresh blood 

 is less than joVo> '■'"'sn it cannot possibly be human blood ; (A) if the 

 diameter is more than -^-sms- 'hen it maybe human blood; {c) if the 

 blood-corpuscles, after exhaustive measurement, give a mean diam- 

 eter of more than a^^'oii' 'hen it is human blood (provided it is not 

 the blood of one of the wild beasts referred to). 



The foregoing applies especially to the diagnosis of fresh blood. 

 With regard to dried blood, it is claimed that this can bf recog- 

 nized just as readily, provided it has dried quickly. Blood that has 

 dried slowly undergoes decomposition, and its morphology cannot 

 be made out. A good liquid for remoistening blood is .Miiller's 

 fluid ; but perhaps the best is Virchow's solution, composed of 

 thirty parts caustic potash and seventy parts water. At least five 

 hundred measurements should be made in order to establish the 

 average diameter of the cells. 



If the corpuscles are spheroidal from absorption of moisture, or 

 crenated from drying, they may still be diagnosed, because such 

 changes are the same in the corpuscles of all animals, and have 

 really their proportionate and corresponding ratio of alteration in 

 form and diminution in size, the range or scale of diminution being 

 always alike in the same animal. 



The red blood-corpuscles that have become spherical from imbibi- 

 tion of liquid have thus presented in Dr. Formad's experiments the fol- 

 lowing average diameters in the various animals : I. Man, j^'^j, inch ; 

 2. guinea-pig, ^gV^ '"ch ; 3. Wolf, ^^ inch ; 4. Dog, 3^^ inch ; 

 5. Rabbit, ^fjJj^ inch ; 6. Ox, yj^^^ inch ; 7. Sheep, -^^^ inch ; 8. 

 Goat, 5t;Vti inch. 



These figures show that the diameter of the artificially spherical 

 corpuscles in each animal is just about one-third less than that of 

 the normal bi-concave or disk-like corpuscles of the same animals. 



The question has long been a mooted one, as to whether the 

 microscope can be depended on to determine positively, or not, that 

 a given si)ecimen of blood is that of a human being. Dr. Formad 

 believes that this can be done, while other microscopists of equal 

 •eminence deny the possibility. 



Vaccination. — That small-pox has greatly declined in Eng- 

 land during the past fifty years is apparent from figures which have 

 been published by Dr. Henry Thorne. From 1S38 to 1842 the 

 deaths from small-pox in England amounted to 57.2 per 100,000; 

 in 1880-84 the death-rate was 6.5 per 100,000. He thinks that 

 vaccination has not only a direct influence in causing this reduc- 

 tion in the number of victims to small-pox, but that it has also a 

 tendency to decrease the liability to the disease of children of vac- 

 cinated parents. In this connection it is interesting to note that 

 TAe Medical Press s\.A\.ts, that, out of the five thousand children born 

 every month in Paris, only a thousand are vaccinated by the medi- 

 cal officers a|ipointed for that purpose. The remaining four thou- 

 sand infants are therefore either vaccinated by private practitioners, 

 or not at all. Seeing, however, that more than half the population 

 apply for and receive gratuitous medical attendance, and that fialf 

 the burials are gratuitous, it is very unlikely that all of the four thou- 

 sand are vaccinated at the cost of the parents. It may fairly be 

 assumed that a large proportion are not vaccinated at all, and that 

 is why small-pox exists as an endemic disease at Paris, and does 

 not disappear, as it has done, to a great extent, in Germany. 



ELECTRICAL SCIENCE. 



Experiments in Proof of the Electro-magnetic Theory of 



Light. 



In his presidential address before the mathematical and physical 

 section of the British Association, Prof. G. F. Fitzgerald dwelt at 

 length on the recent experiments of Hertz in Germany on the prop- 

 agation of electro-magnetic disturbances. These experiments are 

 of so much importance, and go so far toward confirming the electro- 

 magnetic theory of light, that a brief j-dsumi of the subject will not 

 be untimely. 



There have been for years two theories with respect to the action 

 upon each other of quantities of electricity, and of elements of 

 electric current. One held that the various phenomena were caused 

 by direct action at a distance ; the other, that they were due to the 

 action of the intervening medium. With respect to the electro- 

 static phenomena, Faraday's discovery that the capacity of a con- 

 denser varied with different dielectrics between the conducting 

 coatings, made the theory of direct action extremely improbable; 

 and his work, with that of Maxwell, has put the theory of an action 

 of ihe dielectric on a firm foundation. 



With respect to electro-magnetic phenomena, however, the case 

 is different. Maxwell, in his magnificent work on electricity and 

 magnetism, developed the idea that electro-magnetic actions are 

 dependent on the surrounding medium, and one of the results is 

 the electro-magnetic theory of light. But there has been no direct 

 and unquestioned proof that there really is such an action in the 

 dielectric as Maxwell has supposed. To illustrate the fundamental 

 ideas involved, suppose we have a condenser made of two sheets 

 of tinfoil with glass between ; and suppose, further, that we have 

 a battery whose poles may be connected to the coatings of the con- 

 denser. If we suddenly connect the poles to the coatings, there 

 will be a momentary current, which will last only long enough to 

 charge the condenser, probably for only a small fraction of a sec- 

 ond. Now, the general idea was, that there was a current in the 

 battery, and in the wires used to connect it with the condenser; 

 and the result was to charge the two coatings, one with plus, the 

 other with minus, electricity; and there the action stopped. Max- 

 well's idea was, that the current, so long as it lasted, was perfectly 

 continuous, but that in the glass plate the action consisted of a 

 'displacement' of electricity; that is, considering a number of 

 planes drawn through the conductors and through the glass, per- 

 pendicular to the direction of current, the amount of electricity 

 crossing any plane was the same at the same instant, but that in 

 the glass the result was a state of strain, exactly as if a spring were 

 bent. The amount of 'displacement' depends on the displacing 

 force, — the electro-motive force of the battery. When the proper 

 displacement has taken place, all further action ceases, unless the 

 strain is too great, in which case the dielectric breaks down, and 

 we have the well-known phenomenon of disruptive discharge. The 

 amount of displacement determines the charge of the condenser. 

 When the electro-motive force is removed and the coatings joined, 

 the strain in the dielectric relieves itself, producing the discharge. 



If we charge the condenser with an alternating current, we have 

 in the glass continuous displacement currents, first in one direction, 

 then in the other. 



From this fundamental idea of looking to the dielectric for the 

 really important part of the phenomena, Maxwell was led to con- 

 sider the laws by which the vibration of electricity on a small con- 

 ductor would be propagated in the surrounding medium. He 

 found that the equations governing the propagation were essen- 

 tially the same as those deduced from the elastic solid theory of 

 light ; and he found that the velocity of propagation of such a dis- 

 turbance was equal to a certain electrical constant which has 

 several times been determined, and which agrees, within the limit 

 of experimental error, with the value of the velocity of light. He 

 also showed a relation between the specific inductive capacity and 

 index of refraction of substances, which has not been completely 

 proved, but which is suggestively close. 



Here the matter dropped for a while. The theory has been ex- 

 tended, notably by Rowland and Fitzgerald, to account for other 

 phenomena of light, but no experimental evidence of a conclusive 

 nature has been produced. 



