ii8 



SCIENCE. 



[Vol. XIV. No. 341 



relation to it as the sour-milk bacterium has to the curdling of 

 milk. 



Objects of the Ripening of Cream. 



There seem to be two chief objects in ripening cream. It is a 

 matter of experience that the butter will separate more readily from 

 ripened cream, and ihe churning therefore be easier; and it is 

 believed by many that the butter made from ripened cream will 

 keep longer than butter made from sweet cream. A simple expla- 

 nation is suggested, if not warranted, by the facts at hand, and 

 may be of interest to butter-makers. Dr. Babcock of the Wis- 

 consin Agricultural Experiment Station has pointed out, that, 

 shortly after milk is drawn from the cow, there appears in it a fine, 

 inappreciable network of fibres, which produce in the milk a slight 

 thickening somewhat like the clotting of blood, except that it is 

 much less marked. This, which Babcock calls " fibrine," is of an 

 albuminous nature, and will readily putrefy. When the cieam 

 rises to the surface of the milk, a considerable quantity of this so- 

 called fibrine is entangled with it, and is skimmed off with the cream. 

 The butter-globules are enclosed in this fibrine, and in churning 

 they must be shaken out. Now, in the time that the cream is 

 ripening, the numerous bacteria are at work upon this albuminous 

 fibrine, feeding upon it and decomposing it. The breaking- down 

 ■of the fibrine is also assisted by the acid that is formed by the bac- 

 teria, for it is a well-known fact that acid will greatly assist in 

 the solution of materials similar to this fibrine. After the fibrine is 

 thus partly dissolved by the action of the bacteria, the butter-glob- 

 ules will much more readily be shaken free from them, and churn- 

 ing be made easier. 



The keeping-property of the butter is easily explained by the 

 same considerations. There is no doubt that bacteria are the cause 

 of rancidity in butter. Bacteria cannot live upon pure fat, but re- 

 quire for food a certain amount of albuminous matter. It follows 

 that the more albuminous matter there is in the butter, the more 

 readily will they grow, and the quicker will the butter become bad. 

 If the cream is churned before the albuminous fibrine has be- 

 come decomposed, the butter will usually contain more of the 

 fibrine than will butter made from cream after the fibrine has de- 

 composed. Butter made from ripened cream will naturally contain 

 more bacteria than that made from sweet, since the ripened cream 

 itself contains them ; but this is a matter of less importance than 

 the ability of the bacteria to grow and multiply in the butter, and, 

 for reasons above stated, this they can more readily do in butter 

 made from sweet cream. 



From this it would seem that the value of ripening cream de- 

 pends upon the albuminous fibrine that is present in the cream ; 

 -and any process that diminishes this diminishes the necessity of 

 ripening, at least so far as concerns the two objects above men- 

 tioned. Babcock has shown that the quicker the cream rises, the 

 less will be the amount of the fibrine entangled with it ; and that, 

 when cream is separated by a centrifugal machine, a considerable 

 part of the fibrine collects on the drum of the machine, and less in 

 the cream. It would seem, therefore, that there would be less need 

 ■of ripening centrifugal cream than that raised in the more common 

 way. 



A third object attained by ripening cream is to give a certain 

 flavor to the butter which is not obtained in butter made from 

 sweet cream. This is a matter of as much importance to butter- 

 makers as either of the other two, for the value of butter usually 

 depends more upon its taste than upon its keeping-properties. But 

 the relation of the taste of butter to the ripening of the cream, and 

 to the method of handling the butter, is a matter too vague and in- 

 definite at present to warrant definite statements. 



Cleanliness in Dairying. 



It must be remembered that many bacteria are so minute that 

 thousands of them might occupy less space than the point of a 

 needle ; that they multiply so rapidly that millions may be pro- 

 duced in a short time from a single one ; that organic (animal and 

 vegetable) matters, including many forms of what are ordinarily 

 called dirt, are media for them to grow in ; that milk is especially 

 ■adapted to their development, and the most minute quantities of it 

 may serve for their dwelling-place, and furnish food for their rapid 

 .growth; and that they are sure to adhere to the surface or cling 



in the joints of vessels that have contained milk. Bearing all of these 

 facts in mind, the necessity for thorough cleansing of all vessels used 

 in handling milk is apparent. To wash such vessels so that no par- 

 ticles of dirt will remain on the surface or in the joints is extremely 

 difficult. It has been frequently demonstrated that no amount of 

 washing in cold or even warm water will remove all bacteria. It 

 is necessary to use boiling water, and to leave it in the vessels for 

 a considerable time, to destroy the active forms of bacteria that 

 are sure to be present. Even though the active forms may be 

 killed by boiling water in the course of a few minutes, their spores, 

 which correspond to seeds, will resist boiling temperature for a 

 long time. The danger of contamination from spores is not so great 

 but that it may be neglected for all practical purposes, and, uijless 

 the vessels are contaminated with some dangerous bacleria, a 

 thorough washing in boiling water is sufficient. But vessels in 

 which milk is to be kept cannot be properly cleaned by pouring 

 boiling water into one, allowing it to remain there for a few min- 

 utes, and then pouring it into another, and making one heating of 

 the water suffice for the cleaning of several vessels. The last ones 

 thus treated will not be much cleaner, so far as bacteria are con- 

 cerned, than if they were washed with cold water. To clean ves- 

 sels thoroughly, it is necessary to use a higher temperature than that 

 of boiling water, which can be readily obtained by putting them 

 for a few minutes in a hot oven or on a hot stove. If this is thor- 

 oughly done, there is no danger of contamination of milk from the 

 milk-vessels. 



The use of sal-soda in washing milk-vessels is advantageous, 

 because it acts chemically upon fatty matters (grease), and thus 

 helps to remove them and other materials which adhere to the 

 vessels with them. In like manner, the use of " live steam " to 

 " dry " vessels after washing has the advantage of sterilizing 

 them ; i.e., killing the bacteria by the highly heated steam. 



BOOK-REVIEWS. 



The Ice Age in North America and its Bearings upon the Antiq- 

 2iity of Man. By G. F. WRIGHT. New York, Apoleton. 

 8°. $5- 



It may perhaps be questioned whether the time has yet come 

 for a popular presentation of the glacial theory in so detailed a form 

 as is given in Professor Wright's book, for it is still a matter upon 

 which much investigation must be expended ; but, on talking with 

 teachers and intelligent readers who have not access to the scat- 

 tered literature of investigation, it is apparent enough that they 

 greatly need a compendium of the results of glacial study as it now 

 stands, as they have no sufficient comprehension of its remarkable 

 conclusions. This book on the ice age in North America will 

 therefore have a wide reading, and, if its readers note carefully the 

 expressions of doubt as well as the expressions of fact, it must be 

 serviceable to them. Professor Wright's style is entertaining, and 

 he brings together a large and well-selected body of description 

 from the works of pretty much all the glacialists in the country. 

 The illustrations are excellent, and the citations are numerous ; 

 but, for the sake of historical precision, it would have been better to 

 add the date of publication of the writings of others, and it might 

 have been advisable for the author to place the " Report of the 

 Ohio Geological Survey," and several other papers, before his own 

 in the extended list of essays on our terminal moraines (p. 139), to 

 which the studious reader is referred. 



The book opens by discussing the nature of glaciers in general, 

 and illustrates this by descriptions of our glaciers in the West, and 

 by the author's account of his observations on the INluir glacier in 

 Alaska in 1886.' Glaciers in Greenland and other parts of the 

 v/orld are then allowed two chapters before taking up the indica- 

 tions of extinct glacial action, to which the rest of the volume is 

 devoted. Some of the more important headings are, " The Glacial 

 Boundary and Terminal IMoraines," " Glacial Erosion, Transporta- 

 tion, and Deposition ; " " Contrasts of Pre-glacial, Glacial, and 

 Post-glacial Drainage ; " " The Date of the Glacial Period and its 

 Relation to the Antiquity of Man." 



If one may judge by the small attention given to glacial topog- 

 raphy in our ordinary text-books on physical geography, it may be 



