272 



SCIENCE. 



[Vol. XVII. No. 432 



SCIENCE; 



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 *• Exchange " column is likewise open. 



Steps are being taken to celebrate the seventieth birthday of 

 Professor von Helmholtz, which occurs on Aug. 31. A marble 

 bust of Professor Helmholtz is being made, which will be presented 

 to him on that occasion, and a fund is being raised, the income of 

 which is to be applied, primarily, to the bestowal of a Helmholtz 

 medal on eminent investigators of all nations in the fields of Pro- 

 fessor Helmholtz's activity. An international committee, which 

 has been formed to carry out these schemes, solicits contributions, 

 which may be sent to the committee's bankers, Mendelsohn & Co., 

 Berlin. Professor Henry P. Bowditch of Harvard University will 

 forward the contributions of such as mav find it more convenient 

 to send to him, with the names of the contributors, to the bankers 

 appointed by the committee. All contributions should be sent cs 

 soon as possible. 



JULIUS ERASMUS HILGAED. 



Mk. Hilgaed, whose death on May 8 has been announced, was 

 born at Zvs'eibrticken, in Rhenish Bavaria, Jan. 27, 1835. His 

 father vras a man of a wide range of accomplishments, — coun- 

 sellor at law, judge, poet, classical scholar, and author. Being of 

 liberal tendencies in politics, he became dissatisfied with the 

 regime under which he lived, emigrated in 1835, and settled in 

 Illinois, where he personally directed the education of his chil- 

 dren. The subject of the present notice also studied in Philadel- 

 phia, where he made the acquaintance of Professor Bache. In 

 1845 he obtained an appointment in the Coast Survey, and soon 

 became one of Bache's most trusted assistants. 



His administrative and business tact led to his promotion in 

 1863 to the position of assistant in charge of the Coast-Survey 

 Office. He now took a prominent part in directing the scientific 

 work of the survey, especially in its relation to the International 

 Metrical and Geodetic Commissions, having their headquarters in 

 Paris. Perhaps his most noteworthy work was that done in con- 

 nection with the determination of the transatlantic longitude in 

 1872. Soon after the Atlantic cables were put into successful 

 operation, the difi'erence of longitude between Greenwich and the 

 Harvard College Observatory was determined by Dr. B. A. Gould. 

 Shortly afterward the French cable was laid between Brest and 

 St. Pierre, and it was judged expedient to repeat the determina- 

 tion by taking Paris as the starting-point. It happened, howevei', 

 that the telegraphic determination of the longitude of Paris from 

 Greenwich, made in 1853, was very doubtful, and it became a 

 necessary part of Mr. Hilgard's work to repeat this determination. 

 This he did with (he assistance of Mr. Frank Blake, then sub- 



assistant on the survey, who observed both 'at Greenwich and 

 Paris. The result was an important correction to the longitude 

 of Paris, and hence to other European longitudes which depended 

 upon it. 



On each occasion of a vacancy in the superintendency of the 

 Coast Survey, Mr. Hilgard was naturally a prominent candidate 

 for the succession. He was, however, disappointed in his aspira- 

 tions, both on the death of Professor Bache in 1867, and on" the 

 resignation of Professor Peirce in 1874. On the death of Capt. 

 Patterson in 1881, his long and efficient service as assistant in 

 charge of the oflice, and his intimate acquaintance with all the 

 details of the work, made his appointment seem especially fitting; 

 and he was selected for the position with the general concurrence 

 of all parties interested. He had not been long in ofBce before 

 the symptoms of the insidious disease which finally carried him 

 off increased to such a degree that he was obliged to resign in 

 1886. 



Whatever weakness may have been developed in the last years 

 of his life, there can be no two opinions upon the character and 

 value of his life-work in connection with the Coast Survey. He 

 brought into that branch of the public service a rare combination 

 of culture, zeal, knowledge of the world, and executive ability; 

 and no man living will claim to have done more than he did for 

 the character and efficiency of the survey. 



THE FERMENTATIONS OF MILK. AND THEIR PREVEN- 

 TION.' 



Sweet milk is the foundation of the dairy interest. All dairy 

 products are dependent upon milk, and furthermore, they are der 

 pendent upon sweet milk, for after it has undergone any of its 

 fermentative changes it becomes worthless either to be used as 

 milk or in the manufacture of butter or cheese. When'milk i5rst 

 comes to our hands from the cow it is always sweet, and it Tias 

 no tendency to undergo any troublesome changes. But this_con- 

 dition lasts only a short time, and sooner or later some form of 

 decomposition begins, and the milk becomes useless. "It is our 

 purpose, this afternoon, to study some 6f these fermentations and 

 to determine if possible some of tbe facts regarding their preven- 

 tion. It may be well to say at the beginning that I have no royal 

 road to recommend for the prevention of milk fermentations, since 

 no practical method of preventing them has yet been discovered. 

 But a knowledge of the nature of these troublesome changes and 

 of their causes will go far toward enabling each one to guide him- 

 self in avoiding them. 



I shall consider the subject under three heads: 1. What are the 

 fermentations of milk? 2. What are the causes of these' fermen- 

 tations? 3. How may the fermentations be prevented ? 



First, then, we will consider what are these fermentations. We 

 may notice at the outset that they are widely varied. They are 

 by no means confined to the ordinary souring and the fermentation 

 produced by rennet, although these are the only ones that are so 

 well known as to have received special names in tbe dairy. Every- 

 one, however, who has had any extended dealings with milk, has 

 noticed that it sometimes undergoes changes that are quite differ- 

 ent from the normal ones, but which may be none the less trou-, 

 blesome. The various fermentations which are now known to be 

 common to milk have only been recognized within a few years. 

 While the souring of milk has been known for centuries, and the 

 fermentation of milk by the action of rennet has also been long 

 understood, mdk has been studied scientifically only about fifty 

 years. During tbe last fifty years various sorts of decomposition 

 changes have Been recognized, one after another, until to-day the 

 number known is quite large. Let us, then, in introduction to 

 our subject, review briefly the most common forms of fermenta- 

 tion which are liable to occur in milk, taking them partly in the 

 order of the commonness of their occurrence. 



First, we may notice the ordinary souring of milk, though it is 

 too well known to demand description. This effect is connected 

 with the milk sugar present in the milk. The milk sugar under- 

 goes a decomposition and forms lactic acid, the acid thus formed 



1 An address by Professor H. W. Conn, in December, 1890, before the Con- 

 necticut State Board of Agriculture. , ' _ 



