374 ANNUAL OF SCIENTIFIC DISCOVERY. 



prevails as in Acalephs. The secretions of the Tabulata are/ocrt secretions, 

 whilst those of other corals are from the outer walls. 



REVACCINATION. 



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A paper on this subject was recently presented to the Academy 6f Medi- 

 cine of Paris, in the name of Dr. Yleinincks, one of its corresponding mem- 

 bers. The author gives an account of the experiments instituted at Gand by 

 Dr. Denobele, with a view to ascertain the advantages arising from a repeti- 

 tion of vaccination at various periods of life. The results arrived at are, 

 that between the ages of twenty and forty, revaccination only takes effect 

 upon four out of one hundred patients, while the proportion of those on 

 whom it takes effect between the ages of forty and sixty is twenty-three per 

 cent. ; and between the ages of sixty and seventy, fifty-four per cent. The 

 consequences deduced from these facts are: 1. That until the age of twenty- 

 five, revaccination is useless; 2. That from that age to thirty-five it produces 

 useful effects upon a very small number of persons, and that consequently 

 it need not be very strenuously recommended at that period of life; 3. That 

 from the age of thirty -five and upwards it becomes really prophylactic, and 

 therefore necessary; 4. That when vaccination has not taken effect at a cer- 

 tain period, this is no reason for concluding that it will not take effect at 

 some future period. Hence Dr. Yleinincks concludes that the revaccination 

 of the pupils of schools and seminaries, as also of soldiers in the army, is 

 useless. 



THE PARASITE OF A PARASITE. 



An acarus, infesting the parasite of a bee, has been lately discovered, and 

 a photographic portrait of the inject, magnified one million times, surface 

 measurement, has been taken by Mr. A. Bertsch. It is covered with a cara- 

 pace, or hollow shield," and its feet are armed with sharp claws, by which il 

 keeps a firm hold upon the microscopic creature from which it derives nour 

 ishment, and which in its turn preys upon the honey-gathering bee. As we 

 can discover no limits to the minuteness of organized beings, so we can fix 

 no term to this extraordinary series of parasitic animals preying one upon 

 the other. How much further can we hope to fathom the mysteries of 

 organic creation? 



ON THE MIGRATION OF FISHES. 



At a meeting of the Boston Society of Xatural History, Dr. H. R. Storer 

 presented specimens of a smelt, from Squam Lake, N. H., remarking on 

 their peculiar interest, as affording an instance of a species originally migrat- 

 ing to fresh water from salt water, and now permanently resident in the 

 former. He had learned of its existence several years since, but had until 

 now been unable to obtain it. When full grown, the lake smelt seldom 

 exceeds six inches in length, and is extremely attenuated; but a careful 

 examination leaves little doubt of its identity with our marine Osmerus 

 vindescens. It is found throughout the year, in both Squam Lake and Win- 

 nipisseogee, though more rarely in the latter. The modifications in shape 

 referred to would probably be found to exist also in the smelt of Jamaica 

 Pond, near Boston, the conditions of life being much the same in both, the 



